Automatically assemble SPIR-V shaders for the spirv_new suite

Move the SPIR-V assembly helper Python script to the `spirv_asm`
subdirectory.

Add custom commands and targets to automatically assemble and validate
the SPIR-V shaders used by the test.

Automatic assembly depends on finding `python3`, `spirv-as` and
`spirv-val`. `SPIRV_TOOLS_DIR` can be defined by the user during
configuration to provide an override path. Default behaviour assumes
that the binaries exist in PATH.

Signed-off-by: Ahmed Hesham <ahmed.hesham@arm.com>

test_conformance/spirv_new/CMakeLists.txt

@@ -42,3 +42,6 @@ endif()
 set(${MODULE_NAME}_SOURCES ${${MODULE_NAME}_SOURCES} ${TEST_HARNESS_SOURCES})
 
 include(../CMakeCommon.txt)
+
+add_subdirectory(spirv_asm)
+add_dependencies(${${MODULE_NAME}_OUT} spirv_new_shaders)