clocksource: armv8-timer: Make armv8_clocksource_read() static ...

There are no users of that function outside of the driver itself, so
re-declare it as static.

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

clocksource: armv8-timer: Convert explicit assembly into helpers ...

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>

clocksource: Add armv8 generic timer support ...

armv8 has a generic time used in many SoCs. Add support for it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>