Add support for pointer authentication

The previous commit added the infrastructure to load and save
ARMv8.3-PAuth registers during Non-secure <-> Secure world switches, but
didn't actually enable pointer authentication in the firmware.

This patch adds the functionality needed for platforms to provide
authentication keys for the firmware, and a new option (ENABLE_PAUTH) to
enable pointer authentication in the firmware itself. This option is
disabled by default, and it requires CTX_INCLUDE_PAUTH_REGS to be
enabled.

Change-Id: I35127ec271e1198d43209044de39fa712ef202a5
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/include/arch/aarch64/arch_features.h b/include/arch/aarch64/arch_features.h
index da8b6e4..495ecb3 100644
--- a/include/arch/aarch64/arch_features.h
+++ b/include/arch/aarch64/arch_features.h
@@ -23,6 +23,23 @@
 		ID_AA64MMFR2_EL1_CNP_MASK) != 0U;
 }
 
+static inline bool is_armv8_3_pauth_present(void)
+{
+	uint64_t mask = (ID_AA64ISAR1_GPI_MASK << ID_AA64ISAR1_GPI_SHIFT) |
+			(ID_AA64ISAR1_GPA_MASK << ID_AA64ISAR1_GPA_SHIFT) |
+			(ID_AA64ISAR1_API_MASK << ID_AA64ISAR1_API_SHIFT) |
+			(ID_AA64ISAR1_APA_MASK << ID_AA64ISAR1_APA_SHIFT);
+
+	/* If any of the fields is not zero, PAuth is present */
+	return (read_id_aa64isar1_el1() & mask) != 0U;
+}
+
+static inline bool is_armv8_3_pauth_api_present(void)
+{
+	return ((read_id_aa64isar1_el1() >> ID_AA64ISAR1_API_SHIFT) &
+		ID_AA64ISAR1_API_MASK) != 0U;
+}
+
 static inline bool is_armv8_4_ttst_present(void)
 {
 	return ((read_id_aa64mmfr2_el1() >> ID_AA64MMFR2_EL1_ST_SHIFT) &