ARM: SAMSUNG: Move IRQ VIC timer handling out to common header files

Move the VIC based timer interrupt handling out of plat-s3c64xx and
into plat-samsung to be re-used for other systems. This also reduces
the code size as we now have a common init routine and use the irq_desc
to store the interrupt number of the timer.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>