firmware: cs_dsp: Add mock wmfw file generator for KUnit testing

Add a mock firmware file that emulates what the firmware build tools
would normally create. This will be used by KUnit tests to generate a
test wmfw file.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20241212143725.1381013-4-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/firmware/cirrus/test/Makefile

@@ -4,6 +4,7 @@
 cs_dsp_test_utils-objs :=	\
 		cs_dsp_mock_mem_maps.o \
 		cs_dsp_mock_regmap.o \
-		cs_dsp_mock_utils.o
+		cs_dsp_mock_utils.o \
+		cs_dsp_mock_wmfw.o
 
 obj-$(CONFIG_FW_CS_DSP_KUNIT_TEST_UTILS) += cs_dsp_test_utils.o