csky: Sync riscv mm/fault.c for easy maintenance

Sync arch/riscv/mm/fault.c into arch/csky for easy maintenance.
Here are the patches related to the modification:

cac4d1dc "riscv/mm/fault: Move no context handling to no_context()"
ac416a72 "riscv/mm/fault: Move vmalloc fault handling to vmalloc_fault()"
6c11ffbf "riscv/mm/fault: Move fault error handling to mm_fault_error()"
afb8c6fe "riscv/mm/fault: Move access error check to function"
bda281d5 "riscv/mm/fault: Simplify fault error handling"
a51271d9 "riscv/mm/fault: Move bad area handling to bad_area()"

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Palmer Dabbelt <palmerdabbelt@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>