ext: move libmetal to hal

libmetal itself isn't an ipc library, its a generic HAL abstraction
library so move it into ext/hal where it belongs.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>

ext/hal/README

@@ -12,6 +12,10 @@ cmsis
 The ARM Cortex Microcontroller Software Interface Standard (CMSIS) defines a
 set of standard interfaces to ARM Cortex-M SoCs.
 
+libmetal
+--------
+libmetal provides a HAL abstraction layer utilized by open-amp
+
 gecko
 -----
 The Silicon Labs Gecko SDK provides device header files and peripheral drivers

ext/hal/libmetal/libmetal.cmake

@@ -2,7 +2,7 @@ include(ExternalProject)
 
 ExternalProject_Add(
   libmetal                 # Name for custom target
-  SOURCE_DIR $ENV{ZEPHYR_BASE}/ext/lib/ipc/libmetal/
+  SOURCE_DIR $ENV{ZEPHYR_BASE}/ext/hal/libmetal/libmetal/
   INSTALL_COMMAND ""      # This particular build system has no install command
   CMAKE_ARGS -DWITH_ZEPHYR=ON -DBOARD=${BOARD} -DWITH_DEFAULT_LOGGER=OFF -DWITH_DOC=OFF
   )