x86/acpi/cstate: Remove open coded check for cpu_feature_enabled()

acpi_processor_power_init_bm_check() has an open coded implementation
of cpu_feature_enabled() to detect X86_FEATURE_ZEN.

Switch to using cpu_feature_enabled().

Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>