Right now, there are two versions of system_global.h headers.

Both share a lot of common code. There are some ISP2401 specific
types on one of the headers, but it doesn't conflict with the
ISP2400 ones.

Also, the common code is identical.

So, remove code duplication by moving such code into a
common header.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>