target/xtensa: drop num_[core_]regs from dc232b/dc233c configs

Now that xtensa_count_regs does the right thing, remove manual
initialization of these fields from the affected configurations and let
xtensa_finalize_config initialize them. Add XTREG_END to terminate
register lists.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

target/xtensa/core-dc232b.c

@@ -40,8 +40,6 @@
 static XtensaConfig dc232b __attribute__((unused)) = {
     .name = "dc232b",
     .gdb_regmap = {
-        .num_regs = 120,
-        .num_core_regs = 52,
         .reg = {
 #include "core-dc232b/gdb-config.inc.c"
         }