ACPI: CPPC: Add IS_OPTIONAL_CPC_REG macro to judge if a cpc_reg is optional

In ACPI 6.5, s8.4.6.1 _CPC (Continuous Performance Control), whether
each of the per-cpu cpc_regs[] is mandatory or optional is defined.

Since the CPC_SUPPORTED() check is only for optional _CPC fields,
another macro to check if the field is optional is needed.

Reviewed-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://patch.msgid.link/20250411093855.982491-2-zhenglifeng1@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: Lifeng Zheng

drivers/acpi/cppc_acpi.c

@@ -128,6 +128,20 @@ static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);
 #define CPC_SUPPORTED(cpc) ((cpc)->type == ACPI_TYPE_INTEGER ?		\
 				!!(cpc)->cpc_entry.int_value :		\
 				!IS_NULL_REG(&(cpc)->cpc_entry.reg))
+
+/*
+ * Each bit indicates the optionality of the register in per-cpu
+ * cpc_regs[] with the corresponding index. 0 means mandatory and 1
+ * means optional.
+ */
+#define REG_OPTIONAL (0x1FC7D0)
+
+/*
+ * Use the index of the register in per-cpu cpc_regs[] to check if
+ * it's an optional one.
+ */
+#define IS_OPTIONAL_CPC_REG(reg_idx) (REG_OPTIONAL & (1U << (reg_idx)))
+
 /*
  * Arbitrary Retries in case the remote processor is slow to respond
  * to PCC commands. Keeping it high enough to cover emulators where