LoongArch: Cleanup headers to avoid circular dependency

mainline inclusion
from mainline-v6.0-rc3
commit 092e9ebe
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB


CVE: NA

--------------------------------

When enable GENERIC_IOREMAP, there will be circular dependency to cause
build errors. The root cause is that pgtable.h shouldn't include io.h
but pgtable.h need some macros defined in io.h. So cleanup those macros
and remove the unnecessary inclusions, as other architectures do.

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