drm/sysfb: simpledrm: Support power management

drm/sysfb: simpledrm: Support power management

Set PM ops for the simpledrm driver. Suspend and resume the DRM
state on systems that support it.

Many systems lose the hardware's framebuffer settings on suspend,
hence resuming doesn't work there. Yet some systems, most notably
emulators, keep the hardware state across suspend/resume cycles.
There, DRM's suspend and resume helpers bring back the display on
resume.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patch.msgid.link/20260408120722.328769-5-tzimmermann@suse.de