refactor(aarch64): rename do_panic and el3_panic

Current panic call invokes do_panic which calls el3_panic, but now panic
handles only panic from EL3 anid clear separation to use lower_el_panic()
which handles panic from lower ELs.

So now we can remove do_panic and just call el3_panic for all panics.

Change-Id: I739c69271b9fb15c1176050877a9b0c0394dc739
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/bl31/aarch64/runtime_exceptions.S b/bl31/aarch64/runtime_exceptions.S
index 0c60859..cf79361 100644
--- a/bl31/aarch64/runtime_exceptions.S
+++ b/bl31/aarch64/runtime_exceptions.S
@@ -563,7 +563,7 @@
 	 */
 
 	tst	w0, w0
-	b.mi	do_panic	/* negative return value: panic */
+	b.mi	el3_panic	/* negative return value: panic */
 	b.eq	1f		/* zero: do not change ELR_EL3 */
 
 	/* advance the PC to continue after the instruction */