aarch64: support for aarch32 ARM_MODE_UND

Fix:
unrecognized psr mode: 0x1b
cannot read system control register in this mode: (UNRECOGNIZED : 0x1b)

Change-Id: I4dc3e72f90d57e52c0fe63cb59a7529a398757b3

Signed-off-by: Julien Massot <julien.massot@iot.bzh>
Change-Id: Ifa5d21ae97492fde9e8c79ee7d99d8a2a871b1b5
Reviewed-on: https://review.openocd.org/c/openocd/+/6808
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/armv8.c

@@ -77,6 +77,10 @@ static const struct {
 		.name = "HYP",
 		.psr = ARM_MODE_HYP,
 	},
+	{
+		.name = "UND",
+		.psr = ARM_MODE_UND,
+	},
 	{
 		.name = "SYS",
 		.psr = ARM_MODE_SYS,