Add CMake toolchain file for Cortex-M55

This sets the CFLAGS correctly for Cortex-M55 and -Os. This file can be
passed to CMake to allow us to easily build for M55.

Signed-off-by: David Horstmann <david.horstmann@arm.com>

Author: davidhorstmann-arm

platform/arm-gcc-m55.cmake

@@ -0,0 +1,9 @@
+set(CMAKE_SYSTEM_NAME Generic)
+
+set(CMAKE_C_COMPILER arm-none-eabi-gcc)
+# CMAKE_SIZE_UTIL is not a 'real' CMake variable but is sometimes
+# used by convention in embedded toolchain files.
+set(CMAKE_SIZE_UTIL arm-none-eabi-size)
+
+set(CMAKE_C_FLAGS "-mthumb -mcpu=cortex-m55 -Os")
+set(CMAKE_EXE_LINKER_FLAGS "--specs=nosys.specs")