Current implementation of driver has several similar helper functions
for packet format detection in protocol version 2.

This commit merges them as code refactoring.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210623075941.72562-6-o-takashi@sakamocchi.jpSigned-off-by: Takashi Iwai <tiwai@suse.de>