platform/x86: ISST: Check HWP support before MSR access

On some systems, HWP can be explicitly disabled in the BIOS settings
When HWP is disabled by firmware, the HWP CPUID bit is not set, and
attempting to read MSR_PM_ENABLE will result in a General Protection
(GP) fault.

  unchecked MSR access error: RDMSR from 0x770 at rIP: 0xffffffffc33db92e (disable_dynamic_sst_features+0xe/0x50 [isst_tpmi_core])
  Call Trace:
   <TASK>
   ? ex_handler_msr+0xf6/0x150
   ? fixup_exception+0x1ad/0x340
   ? gp_try_fixup_and_notify+0x1e/0xb0
   ? exc_general_protection+0xc9/0x390
   ? terminate_walk+0x64/0x100
   ? asm_exc_general_protection+0x22/0x30
   ? disable_dynamic_sst_features+0xe/0x50 [isst_tpmi_core]
   isst_if_def_ioctl+0xece/0x1050 [isst_tpmi_core]
   ? ioctl_has_perm.constprop.42+0xe0/0x130
   isst_if_def_ioctl+0x10d/0x1a0 [isst_if_common]
   __se_sys_ioctl+0x86/0xc0
   do_syscall_64+0x8a/0x100
   entry_SYSCALL_64_after_hwframe+0x78/0xe2
  RIP: 0033:0x7f36eaef54a7

Add a check for X86_FEATURE_HWP before accessing the MSR. If HWP is
not available, return true safely.

Fixes: 12a7d2c ("platform/x86: ISST: Add SST-CP support via TPMI")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20260303074635.2218-1-lirongqing@baidu.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: lrq-max

drivers/platform/x86/intel/speed_select_if/isst_tpmi_core.c

@@ -558,6 +558,9 @@ static bool disable_dynamic_sst_features(void)
 {
 	u64 value;
 
+	if (!static_cpu_has(X86_FEATURE_HWP))
+		return true;
+
 	rdmsrq(MSR_PM_ENABLE, value);
 	return !(value & 0x1);
 }