ARM: remove mrc_opcode(), use MRC() or MCR()

ARM: remove mrc_opcode(), use MRC() or MCR()

Get rid of mrc_opcode() in favor of ARMV4_5_MRC() or, where
arm*20t should have used it, ARMV4_5_MCR() instead.

Basically, *writing* coprocessor registers shouldn't have
used the *read* opcode ... and both should stick to standard
opcode constructors, not rearranging parameter sequence any
more than already needed.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>