arm64: cpufeature: Avoid warnings due to unused symbols

An allnoconfig build complains about unused symbols due to functions
that are called via conditional cpufeature and cpu_errata table entries.

Annotate these as __maybe_unused if they are likely to be generic, or
predicate their compilation on the same option as the table entry if
they are specific to a given alternative.

Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/cpu_errata.c

@@ -285,8 +285,8 @@ qcom_enable_link_stack_sanitization(const struct arm64_cpu_capabilities *entry)
  * of call backs, sharing the same capability bit.
  * Iterate over each entry to see if at least one matches.
  */
-static bool multi_entry_cap_matches(const struct arm64_cpu_capabilities *entry,
-				    int scope)
+static bool __maybe_unused
+multi_entry_cap_matches(const struct arm64_cpu_capabilities *entry, int scope)
 {
 	const struct arm64_cpu_capabilities *caps;
 
@@ -301,7 +301,7 @@ static bool multi_entry_cap_matches(const struct arm64_cpu_capabilities *entry,
  * Take appropriate action for all matching entries in the shared capability
  * entry.
  */
-static void
+static void __maybe_unused
 multi_entry_cap_cpu_enable(const struct arm64_cpu_capabilities *entry)
 {
 	const struct arm64_cpu_capabilities *caps;