LoongArch: mm: Add page table mapped mode support for virt_to_page()

According to LoongArch documentations, there are two types of address
translation modes: direct mapped address translation mode (DMW mode) and
page table mapped address translation mode (TLB mode).

Currently, virt_to_page() only supports direct mapped mode. This patch
determines which mode is used, and adds corresponding handling functions
for both modes.

For more details on the two modes, see [1].

[1] https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#virtual-address-space-and-address-translation-mode



Signed-off-by: Enze Li <lienze@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>