ARM: OMAP2+: PRM: remove unnecessary cpu_is_XXX calls from prm_init / exit

Done in preparation to make PRM its own driver, as the cpu_is_XXX calls are
not available outside mach-omap2 folder.

The init functions are called only from cpu specific init chain, and thus
don't need to double check against cpu type.

The exit calls check against the data provided during init-time registration
and thus don't need cpu check either.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
[paul@pwsan.com: updated to apply]
Signed-off-by: Paul Walmsley <paul@pwsan.com>