media: Documentation: ccs: Rename ccs-regs.txt as ccs-regs.asc

As documentation used to be in .txt files before converting to ReST,
rename ccs-regs.txt to avoid it being taken as documentation that
pre-dates ReST conversion and so target for further conversion to ReST.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>