graphics/drm-kmod: Bump PORTREVISION after update

While here fix _DRM_ARCHS for 14.0/15-CURRENT

Reported by:	cpercival
Fixes:		4df670b4 ("graphics/drm-kmod: Set default version for 15-CURRENT to 6.1-lts")
Sponsored by:	Beckhoff Automation GmbH & Co. KG