AArch64: Unify relocation restrictions between MOVK/MOVN/MOVZ.

There doesn't seem to be a practical reason for these instructions to have
different restrictions on the types of relocations that they may be used
with, notwithstanding the language in the ELF AArch64 spec that implies that
specific relocations are meant to be used with specific instructions.

For example, we currently forbid the first instruction in the following
sequence, despite it currently being used by clang to generate a global
reference under -mcmodel=large:

	movz	x0, #:abs_g0_nc:foo
	movk	x0, #:abs_g1_nc:foo
	movk	x0, #:abs_g2_nc:foo
	movk	x0, #:abs_g3:foo

Therefore, allow MOVK/MOVN/MOVZ to accept the union of the set of relocations
that they currently accept individually.

Differential Revision: https://reviews.llvm.org/D64466

llvm-svn: 366461