ARM: OMAP4: Export omap4_get_base*() rather than global address pointers

This patch exports APIs to get base address for GIC
distributor, CPU interface, SCU and PL310 L2 Cache which
are used in OMAP4 PM code.

This was suggested by Kevin Hilman <khilman@ti.com> during
OMAP4 PM code review.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Jean Pihet <j-pihet@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Tested-by: Vishwanath BS <vishwanath.bs@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>