ARM: EXYNOS: add a register base address variable in mct controller driver

All the MCT register read/writes use a fixed remapped address
S5P_VA_SYSTIMER.  With device tree support for MCT controller,
it is possible to remove the static remap of the MCT controller
address space and do the remap during the initialization of the
MCT controller with the physical address obtained from the device
tree.

So in preparation of adding device tree support for MCT controller,
add a new register base address variable that will hold the remapped
MCT controller base address and convert all MCT register read/writes
to use this new variable as the base address instead of the fixed
S5P_VA_SYSTIMER.

While at it, the MCT register offset and bit mask definitions are
moved into the MCT controller driver file since there are no other
consumers of these definitions.

Cc: Changhwan Youn <chaos.youn@samsung.com>
Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>