amdgcn: Clean up the mov insn definitions

amdgcn: Clean up the mov insn definitions

This patch should not change anything functional; it just deletes some cruft
and converts the constraints to the new format.  This is to make it easier
to edit later.

 * The long-commented-out insns are now deleted.
 * The vestigial support for unaligned register pairs has been removed (it
 was disabled and removed elsewhere long ago).

gcc/ChangeLog:

	* config/gcn/gcn-valu.md (*mov<mode>_exec_match): Delete.
	(*mov<mode>_exec_match): Likewise.
	(*mov<mode>): Delete unaligned register support, and convert to new
	constraint syntax.
	(mov<mode>_exec): Likewise.
	(@mov<mode>_sgprbase): Likewise.
	* config/gcn/gcn.md (*movbi): Likewise.