media: rkvdec: Introduce a global bitwriter helper

media: rkvdec: Introduce a global bitwriter helper

The use of structures with bitfields is good when the values are
somewhat aligned.
More mis-alignement means that compilers need to do more gymnastics
to edit the fields values.

Some cases have been reported with CLang on specific architectures
like armhf and hexagon, where the compiler would allocate a bigger
local stack than needed or even completely freeze during compilation.

Some fixes have been provided to ease the issues, but the real fix
here is to use a bitwriter instead of heavily unaligned bitfields.

This is a preparation commit to provide a global bitwriter interface
for the whole driver.

Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>