target/armv8: do not mark ELx banked regs as save-restore

GDB uses this mark when creating a dummy frame for
manual call of a function by GDB command.

With the original setting of all registers as caller_save = true
GDB inferior call fails in EL2H mode with the message
Could not fetch register "ELR_EL3"; remote failure reply '0E'

It also fails similarly in EL0 and EL1 modes.

A standard function should not change EL banked registers anyway.
Avoid marking ELx banked registers as save-restore.

Treat pauth_dmask and pauth_cmask registers similarly.
They are not typically changed in a function.

Change-Id: Ibaf32210f3fcfa9dfb15e924b888243460e85fb4
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/9243
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/armv8.c

@@ -1855,7 +1855,12 @@ struct reg_cache *armv8_build_reg_cache(struct target *target)
 		reg_list[i].group = armv8_regs[i].group;
 		reg_list[i].number = i;
 		reg_list[i].exist = true;
-		reg_list[i].caller_save = true;	/* gdb defaults to true */
+
+		/* Registers which should be preserved across GDB inferior function calls.
+		 * Avoid saving ELx banked registers as a standard function should
+		 * not change them and higher EL registers are not accessible
+		 * in lower EL modes. */
+		reg_list[i].caller_save = i < ARMV8_ELR_EL1;
 
 		feature = calloc(1, sizeof(struct reg_feature));
 		if (feature) {