ARM: set arch_gettimeoffset directly

remove ARM's struct sys_timer .offset function pointer, and instead
directly set the arch_gettimeoffset function pointer when the timer
driver is initialized. This requires multiplying all function results
by 1000, since the removed arm_gettimeoffset() did this. Also,
s/unsigned long/u32/ just to make the function prototypes exactly
match that of arch_gettimeoffset.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Andrew Victor <linux@maxim.org.za>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc: Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ryan Mallon <rmallon@gmail.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>