added hpd fsm. not sure if compliant with the standard.
hdmi_in is the only allowed to srst the fsm.
on lock loss (e.g. resolution change)
hdmi_out is checked only after hdmi_in is locked, just once
so, if hdmi_out is disconnected, design will continue tx
design requires both FPGA .bit and PS7 .elf, to work correctly
previous commit needs both FPGA and PS7 as well.
neyko3
7a183c9aee