disp/nv50: Add method for probing active heads
pwr/memx/nva3: Implement "wait for VBLANK"
pwr/memx: Make FB disable and enable explicit

Needs to be done after wait-for-VBLANK, and NVA3 requires register writes in between. Rather than hard-coding register writes, just split out fb_disable and fb_enable.
fb/ramnve0: Disable FB before reclocking

This used to be done implicitly
pwr/memx: Return execution time
pwr/memx: Match blobs behaviour
fb/nva3: WIP Start on some reclocking bits
WIP train external hook
fb/ramnva3: WIP support for DDR2 reclocking
fb/ramfuc: Support strided regs
fb/ramnva3: WIP Per-partition regs
fb/ramnva3: Initialise PART_PM_SEL
nv50/display: Set VBLANK time in modeset script

Solves blinking on reclocking memory. The value set is an underestimate, but better than nothing
fb/ramnva3: Try to avoid flicker on reclocking
pwr/nva3: DROP: regenerate microcode