This improves compatibility with some consumer (LG WebOS) TVs which apparently
search a HEVC descriptor (which our mpegts muxer can't generate) or a format
identifier.

Since the HEVC format identifier is not registered (but used in the wild), it is
not written if strict_std_compliance is higher than normal.

This fixes the issue in ticket #7744.
Signed-off-by: Marton Balint <cus@passwd.hu>