ARM: shmobile: R-Car: Get rid of on_off_fn() function pointer

Simplify the power request code by passing an "on" flag, and picking the
right status bit and register offset in the innermost function, based on
this flag.
This allows to remove the rcar_sysc_pwr_{off,on}() helper functions, and
the function pointer through which they were called.

Make sr_bit and reg_offs unsigned while we're at it.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>