x86/cstate: Allow ACPI C1 FFH MWAIT use on Hygon systems
Hygon systems support the MONITOR/MWAIT instructions and these can be
used for ACPI C1 in the same way as on AMD and Intel systems.
The BIOS declares a C1 state in _CST to use FFH and CPUID_Fn00000005_EDX
is non-zero on Hygon systems.
Allow ffh_cstate_init() to succeed on Hygon systems to default using FFH
MWAIT instead of HALT for ACPI C1.
Signed-off-by: Pu Wen <puwen@hygon.cn>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210528081417.31474-1-puwen@hygon.cn