LoongArch: Flush TLB earlier at initialization

Move local_flush_tlb_all() earlier (just after setup_ptwalker() and
before page allocation). This can avoid stale TLB entries misguiding
the later page allocation. Without this patch the second kernel of
kexec/kdump fails to boot SMP.

BTW, move output_pgtable_bits_defines() into tlb_init() since it has
nothing to do with tlb handler setup.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>