[ARM] 4591/1: ns9xxx: simplify REGSET, REGGET and introduce ..._IDX variants

The semantic of the REGSET macros didn't change, but hopefully
it's more obvious as it's now.

REGGET is changed to return the unshifted value, analogous to
REGSET.  REGGETIM behaves as REGGET before.  All callers changed.

..._IDX is used to work with registers that need a parameter like
BBU_GCONFb1.

Signed-off-by: Uwe Kleine-König <ukleinek@informatik.uni-freiburg.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>