gdb: aarch64: Move MTE address check out of set_memtag

gdb: aarch64: Move MTE address check out of set_memtag

Remove check in parse_set_allocation_tag_input as it is redundant:
currently the check happens at the end of parse_set_allocation_tag_input
and also in set_memtag (called after parse_set_allocation_tag_input).

After it, move MTE address check out of set_memtag and add this check to
the upper layer, before set_memtag is called.

This is a preparation for using a target hook instead of a gdbarch hook
on MTE address checks.

Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
Approved-By: Luis Machado <luis.machado@arm.com>