vc_dispmanx: Fix vsync service use counting
vc_dispmanx: Fix vsync service use counting

Correctly maintain an outstanding use count while vsync are being
delivered, and allow update and vsync callbacks to coexist.

luked99/userland-1,adamheinrich/userland,maxnet/userland,maroviher/userland,erlerobot/rpi-userland,ethanol100/userland,maxnet/userland,raspberrypi/userland,raspberrypi/userland,DexterInd/userland,JamesH65/userland,hyunkim9123/userland,maroviher/userland,kraj/userland,gonzoua/userland,adamheinrich/userland,salih/userland,ethanol100/userland,JamesH65/userland,gonzoua/userland,yzhahn/userland,JamesH65/userland,popcornmix/userland,StealthMicro/userland,fredericofs/userland,luked99/userland-1,luked99/userland-1,DexterInd/userland,raspberrypi/userland,adamheinrich/userland,d3faultdotxbe/raspivid-accurate-fps-via-hacky-framedropping,FIIT-TNL/userland,kraj/userland,FIIT-TNL/userland,popcornmix/userland,d3faultdotxbe/raspivid-accurate-fps-via-hacky-framedropping,d3faultdotxbe/raspivid-accurate-fps-via-hacky-framedropping,d3faultdotxbe/raspivid-accurate-fps-via-hacky-framedropping,hyunkim9123/userland,erlerobot/rpi-userland,fredericofs/userland,roberttidey/userland,StealthMicro/userland,oniongarlic/userland,gonzoua/userland,yzhahn/userland,hyunkim9123/userland,erlerobot/rpi-userland,6by9/userland,popcornmix/userland,maxnet/userland,roberttidey/userland,DexterInd/userland,oniongarlic/userland,salih/userland,ethanol100/userland,StealthMicro/userland,fredericofs/userland,yzhahn/userland,maroviher/userland,6by9/userland,roberttidey/userland,6by9/userland,salih/userland,FIIT-TNL/userland,kraj/userland,oniongarlic/userland