x86: remove @return doc for void functions

For functions returning nothing, there is no need to document
with @return, as Doxgen complains about "documented empty
return type of ...".

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

arch/x86/core/cache.c

@@ -26,8 +26,6 @@
  * both is optimal.
  *
  * The cache line size is specified via the d-cache-line-size DTS property.
- *
- * @return N/A
  */
 static void arch_dcache_flush(void *start_addr, size_t size)
 {

arch/x86/core/ia32/excstub.S

@@ -45,8 +45,6 @@
  * created by this routine to determine the locations of volatile registers.
  * These tools must be updated to reflect any changes to the stack frame.
  *
- * @return N/A
- *
  * C function prototype:
  *
  * void _exception_enter(uint32_t error_code, void *handler)

arch/x86/core/ia32/float.c

@@ -50,13 +50,10 @@
 extern uint32_t _sse_mxcsr_default_value;
 
 /**
- *
  * @brief Disallow use of floating point capabilities
  *
  * This routine sets CR0[TS] to 1, which disallows the use of FP instructions
  * by the currently executing thread.
- *
- * @return N/A
  */
 static inline void z_FpAccessDisable(void)
 {
@@ -73,15 +70,12 @@ static inline void z_FpAccessDisable(void)
 
 
 /**
- *
  * @brief Save non-integer context information
  *
  * This routine saves the system's "live" non-integer context into the
  * specified area.  If the specified thread supports SSE then
  * x87/MMX/SSEx thread info is saved, otherwise only x87/MMX thread is saved.
  * Function is invoked by FpCtxSave(struct k_thread *thread)
- *
- * @return N/A
  */
 static inline void z_do_fp_regs_save(void *preemp_float_reg)
 {
@@ -92,15 +86,12 @@ static inline void z_do_fp_regs_save(void *preemp_float_reg)
 }
 
 /**
- *
  * @brief Save non-integer context information
  *
  * This routine saves the system's "live" non-integer context into the
  * specified area.  If the specified thread supports SSE then
  * x87/MMX/SSEx thread info is saved, otherwise only x87/MMX thread is saved.
  * Function is invoked by FpCtxSave(struct k_thread *thread)
- *
- * @return N/A
  */
 static inline void z_do_fp_and_sse_regs_save(void *preemp_float_reg)
 {
@@ -111,12 +102,9 @@ static inline void z_do_fp_and_sse_regs_save(void *preemp_float_reg)
 }
 
 /**
- *
  * @brief Initialize floating point register context information.
  *
  * This routine initializes the system's "live" floating point registers.
- *
- * @return N/A
  */
 static inline void z_do_fp_regs_init(void)
 {
@@ -124,12 +112,9 @@ static inline void z_do_fp_regs_init(void)
 }
 
 /**
- *
  * @brief Initialize SSE register context information.
  *
  * This routine initializes the system's "live" SSE registers.
- *
- * @return N/A
  */
 static inline void z_do_sse_regs_init(void)
 {

arch/x86/core/ia32/intstub.S

@@ -56,8 +56,6 @@
  * created by this routine to determine the locations of volatile registers.
  * These tools must be updated to reflect any changes to the stack frame.
  *
- * @return N/A
- *
  * C function prototype:
  *
  * void _interrupt_enter(void *isr, void *isr_param);

include/arch/x86/ia32/arch.h

@@ -115,9 +115,6 @@ typedef struct s_isrList {
  * @param p IRQ priority
  * @param v Interrupt Vector
  * @param d Descriptor Privilege Level
- *
- * @return N/A
- *
  */
 
 #define NANO_CPU_INT_REGISTER(r, n, p, v, d) \