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

arch/x86/kernel/acpi/cstate.c

@@ -197,7 +197,8 @@ static int __init ffh_cstate_init(void)
 	struct cpuinfo_x86 *c = &boot_cpu_data;
 
 	if (c->x86_vendor != X86_VENDOR_INTEL &&
-	    c->x86_vendor != X86_VENDOR_AMD)
+	    c->x86_vendor != X86_VENDOR_AMD &&
+	    c->x86_vendor != X86_VENDOR_HYGON)
 		return -1;
 
 	cpu_cstate_entry = alloc_percpu(struct cstate_entry);