kselftest/arm64: Ignore check_gcr_el1_cswitch binary

We added check_gcr_el1_cswitch but did not ignore the generated binary,
add it.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210728173539.6231-1-broonie@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/mte/.gitignore

 check_buffer_fill
+check_gcr_el1_cswitch
 check_tags_inclusion
 check_child_memory
 check_mmap_options