Move inline assembly related to querying and counter value as well as
getting and setting counter frequency register into asm/system.h as
well as converting it inot helper functions. This is done to make the
code availible to other parts of the system.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>