Convert ARMs timer implementations to use readl/writel instead of accessing
the registers via a struct.

People have recently asked if accessing timers via a structure is the
"right way" and its not the Linux way.  So fix this code to conform to
"The Linux Way"(tm).
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>