[LoongArch] Insert nops and emit align reloc when handle alignment directive (#72962)

Refer to RISCV, we will fix up the alignment if linker relaxation
changes code size and breaks alignment. Insert enough Nops and emit
R_LARCH_ALIGN relocation type so that linker could satisfy the alignment
by removing Nops.
It does so only in sections with the SHF_EXECINSTR flag.

In LoongArch psABI v2.30, R_LARCH_ALIGN requires symbol index. The
lowest 8 bits of addend represent alignment and the other bits of addend
represent the maximum number of bytes to emit.