arm64: zynqmp: Enable SLG gpo driver by default

This device is used on SOM CCs that's why enable it by default.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/ebbfc0c883ca7d4f70c75d8d3655aaa6a81d77be.1656943737.git.michal.simek@amd.com