MIPS: Add support for Desktop Management Interface (DMI)

Enable DMI scanning on the MIPS architecture, this setups DMI identifiers
(dmi_system_id) for printing it out on task dumps and prepares DIMM entry
information (dmi_memdev_info) from the SMBIOS table. With this patch, the
driver can easily match various of mainboards.

In the SMBIOS reference specification, the table anchor string "_SM_" is
present in the address range 0xF0000 to 0xFFFFF on a 16-byte boundary,
but there exists a special case for Loongson platform, when call function
dmi_early_remap, it should specify the start address to 0xFFFE000 due to
it is reserved for SMBIOS and can be normally access in the BIOS.

This patch works fine on the Loongson 3A3000 platform which belongs to
MIPS architecture and has no influence on the other architectures such
as x86 and ARM.

Additionally, in order to avoid the unknown risks on the mips platform
which is not MACH_LOONGSON64, the DMI config is better to depend on
MACH_LOONGSON64. If other mips platform also needs this DMI feature in
the future, the "depends on" condition can be modified.

Co-developed-by: Yinglu Yang <yangyinglu@loongson.cn>
Signed-off-by: Yinglu Yang <yangyinglu@loongson.cn>
[jiaxun.yang@flygoat.com: Refine definitions and Kconfig]
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Reviewed-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>