8909w:[cherry-pick-override] Fix compilation error for adc kernel test

Add msm_adc.h file and update Kbuild file to fix kernel-test
adc compilation error.

Change-Id: If1c6c3e0b0008acf7e3381943ee711b184b37eab
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>