aarch64: Add new relocations and limit COFF AArch64 relocation offsets

aarch64: Add new relocations and limit COFF AArch64 relocation offsets

The patch adds support for the IMAGE_REL_ARM64_REL32 coff relocation
type. This is needed for 32-bit relative address.

It also adds a check for relocation offsets over 21 bits. Offsets
inside coff files are stored in instruction code. In the case of ADRP
the actual value is stored, not a downshifted page offset. This means
values over 21 bits would otherwise be truncated.

Finally it adds a mapping for BFD_RELOC_AARCH64_ADR_GOT_PAGE and
BFD_RELOC_AARCH64_LD64_GOT_LO12_NC that were previously skipped.

ChangeLog:

	* bfd/coff-aarch64.c (coff_aarch64_reloc_type_lookup): Add
	BFD_RELOC_AARCH64_ADR_GOT_PAGE,
	BFD_RELOC_AARCH64_LD64_GOT_LO12_NC and IMAGE_REL_ARM64_REL32
	relocations.
	(coff_pe_aarch64_relocate_section): Likewise.
	* gas/write.c (adjust_reloc_syms): COFF AArch64 relocation
	offsets need to be limited to 21bits
	(defined): Likewise.