ARM: OMAP3/4: PRM: add support of late_init call to prm_ll_ops

SoC specific late_init call is now registered during PRM init, and will
be called automatically by PRM core. This helps to get rid of some
redundant initcalls and cpu_is_X checks from the PRM code.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>