This way they can be reused by other code without including the whole
decoder-specific hevcdec.h
Also, add the HEVC_ prefix to them, since similarly named values exist
for H.264 as well and are sometimes used in the same code.
Somehow 2 different identifiers have come into existence which makes supporting
both until the next major version bump required
I did not investigate how exactly that did happen.
wm4, j-b and smarter prefer hevc.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>