LoongArch: Use static defined zero page rather than allocated

On LoongArch system, there is only one page needed for zero page (no
cache synonyms), and there is no COLOR_ZERO_PAGE, so zero_page_mask is
useless and the macro __HAVE_COLOR_ZERO_PAGE is not necessary.

Like other popular architectures, It is simpler to define the zero page
in kernel BSS code segment rather than dynamically allocate.

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

LoongArch: Add Non-Uniform Memory Access (NUMA) support

Add Non-Uniform Memory Access (NUMA) support for LoongArch. LoongArch
has 48-bit physical address, but the HyperTransport I/O bus only support
40-bit address, so we need a custom phys_to_dma() and dma_to_phys() to
extract the 4-bit node id (bit 44~47) from Loongson-3's 48-bit physical
address space and embed it into 40-bit. In the 40-bit dma address, node
id offset can be read from the LS7A_DMA_CFG register.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>