UAC1: Add configfs attribute for changing ep max packet size

Currently UAC1 driver is setting to 200 which works in case of
2 channels and sample size of 16 bits. If sample size is changed
to 24 from 16, needs to change endpoint max packet size to fix
audio quality issues. Hence add configfs attribute through which it
can be changed before switching UAC composition.

Change-Id: I8061a9bed4a8894543399cf95cdb60b6ead97e62
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>