Add xf86CursorResetCursor, which allows switching between HW and SW
cursor depending on the current state.
Call it from xf86DisableUnusedFunctions, which is called after any CRTC
configuration change such as setting a mode or disabling a CRTC. This
makes sure that SW cursor is used e.g. while a transform is in use on
any CRTC or while there are active PRIME output slaves, and enables HW
cursor again once none of those conditions are true anymore.
Reviewed-by: Keith Packard <keithp@keithp.com>