target/loongarch: Add PTW feature support in KVM mode

Implement Hardware page table walker(PTW for short) feature in KVM mode.
Use OnOffAuto type variable ptw to check the PTW feature. If the PTW
feature is not supported on KVM host, there is error reported with ptw=on
option.

By default PTW feature is disabled on la464 CPU type, and auto detected
on max CPU type.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>
3 files changed