x11/nvidia-driver: disable GSP Firmware by default

Users have reported issues with suspend/resume when GSP firmware is
enabled. This change disables GSP to unbreak desktop use cases while
a fix is delivered in a future driver version

PR: 285803
Reviewed by: Tomoaki AOKI <junchoon@dec.sakura.ne.jp>
Approved by: kbowling (mentor)
Differential Revision: https://reviews.freebsd.org/D49828