fix(lib/s2tt) : PA must be <= 48 bits for LPA2 disabled Realm

If FEAT_LPA2 is disabled for the realm, add a check to
ensure that PA for some args of RTT related commands is
within 48 bits.

Change-Id: If1647a1848823e63cccf07f46876367c165ef8a5
Signed-off-by: Shruti Gupta <shruti.gupta@arm.com>
diff --git a/lib/s2tt/src/s2tt.c b/lib/s2tt/src/s2tt.c
index 3ad094c..0cde136 100644
--- a/lib/s2tt/src/s2tt.c
+++ b/lib/s2tt/src/s2tt.c
@@ -563,6 +563,8 @@
 	 * Test that all fields that are not controlled by the host are zero
 	 * and that the output address is correctly aligned. Note that
 	 * the host is permitted to map any physical address outside PAR.
+	 * Note that this also checks for the case when FEAT_LPA2 is disabled
+	 * for the Realm, then the PA in `s2tte` must be <= 48 bits wide.
 	 */
 	if ((s2tte & ~mask) != 0UL) {
 		return false;