LoongArch: Support PC-relative relocations in modules

Binutils >= 2.40 uses R_LARCH_B26 instead of R_LARCH_SOP_PUSH_PLT_PCREL,
and R_LARCH_PCALA* instead of R_LARCH_SOP_PUSH_PCREL.

Handle R_LARCH_B26 and R_LARCH_PCALA* in the module loader. For R_LARCH_
B26, also create a PLT entry as needed.

Tested-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>