hevc: fix PTL parsing

This was broken in commit 36658c978f5d7df2ce556075946f3a80f7eca753
hevc: don't check for errors in PTL code

The value of XXX_reserved_zero_44bits should be ignored, no need to
report an error when it's not zero.
hevc: remove unused PTL flags
hevc: pack PTL representation using uint8_t
hevc: rename ptl structs and variables