LoongArch: bfd: Add support for tls le relax.

LoongArch: bfd: Add support for tls le relax.

Add tls le relax support and related relocs in bfd.

New relocation related explanation can refer to the following url:
https://github.com/loongson/la-abi-specs/blob/release/laelf.adoc

This support does two main things:

1. Implement support for three new relocation items in bfd.

The three new relocation items are shown below:

R_LARCH_TLS_LE_ADD_R
R_LARCH_TLS_LE_HI20_R
R_LARCH_TLS_LE_LO12_R

2. ADD a new macro RELOCATE_TLS_TP32_HI20

Handle problems caused by symbol extensions in TLS LE, The processing
is similar to the macro RELOCATE_CALC_PC32_HI20 method.

3. Implement the tls le relax function.

bfd/ChangeLog:

	* bfd-in2.h: Add relocs related to tls le relax.
	* elfnn-loongarch.c:
	(loongarch_relax_tls_le): New function.
	(RELOCATE_TLS_TP32_HI20): New macro.
	(loongarch_elf_check_relocs): Add new reloc support.
	(perform_relocation): Likewise.
	(loongarch_elf_relocate_section): Handle new relocs related to relax.
	(loongarch_elf_relax_section): Likewise.
	* elfxx-loongarch.c:
	(LOONGARCH_HOWTO (R_LARCH_TLS_LE_ADD_R)): New reloc how to type.
	(LOONGARCH_HOWTO (R_LARCH_TLS_LE_HI20_R)): Likewise.
	(LOONGARCH_HOWTO (R_LARCH_TLS_LE_LO12_R)): Likewise.
	* libbfd.h: Add relocs related to tls le relax.
	* reloc.c: Likewise.