mach-ux500: explicit enable MTU TCR in the kernel

PRCM_TCR enables the various timers in the system. This must be achieved
before any of the MTUs are usable for kernel usage. Explicit enabling of
this in the kernel makes it independent of bootloader actions.

Signed-off-by: Sundar Iyer <sundar.iyer@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>