arm64: gitignore: ignore relacheck

Add the generated executable for relacheck to the list of ignored files.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/r/20240222210441.33142-1-brgl@bgdev.pl
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>