This patch enables SPI4 on the 96Boards STM32 Sensors Mezzanine.
SPI4 has been broken out to a Grove Connector on the board.
Changes:
- Updated board dts to enable spi4
- Updated board Kconfig
- Updated board documentation
- Update board pinmux
- Updated stm32f4 pinmux header file
- Updated stm32f401 dtsi
- Updated stm32f4 defconfig to enable PORTE GPIO
- Added board to spi_loopback test
Test: spi_loopback test passed
Signed-off-by: Sahaj Sarup <sahaj.sarup@linaro.org>