aarch64: enable aarch32 debugging with arm gdb

When a PE is in Aarch32 state and gdb asks for a target description,
provide a register view compatible with the "org.gnu.gdb.arm.core"
feature. Only current-mode registers are exported, banked registers are
not visible.

Change-Id: I99a85d94831cf597fe8cff6a0a1818ce0a33613b
Signed-off-by: Matthias Welwarsky <matthias.welwarsky@sysgo.com>

src/target/aarch64.c

@@ -590,6 +590,7 @@ static int aarch64_internal_restart(struct target *target, bool slave_pe)
 
 	/* registers are now invalid */
 	register_cache_invalidate(arm->core_cache);
+	register_cache_invalidate(arm->core_cache->next);
 
 	return ERROR_OK;
 }