arm64: cpufeature: Expose get_arm64_ftr_reg() outside cpufeature.c

get_arm64_ftr_reg() returns the properties of a system register based
on its instruction encoding.

This is needed by erratum workaround in cpu_errata.c to modify the
user-space visible view of id registers.
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20220909165938.3931307-3-james.morse@arm.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/cpufeature.h

@@ -907,6 +907,8 @@ static inline unsigned int get_vmid_bits(u64 mmfr1)
 	return 8;
 }
 
+struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id);
+
 extern struct arm64_ftr_override id_aa64mmfr1_override;
 extern struct arm64_ftr_override id_aa64pfr0_override;
 extern struct arm64_ftr_override id_aa64pfr1_override;

arch/arm64/kernel/cpufeature.c

@@ -750,7 +750,7 @@ static struct arm64_ftr_reg *get_arm64_ftr_reg_nowarn(u32 sys_id)
  * returns - Upon success,  matching ftr_reg entry for id.
  *         - NULL on failure but with an WARN_ON().
  */
-static struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id)
+struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id)
 {
 	struct arm64_ftr_reg *reg;