alsa_sound: Add support for flexible buffer size for recording

- In the current implementation, all the read calls to the driver
  are limited to 320 bytes only. This results performance overhead
  for recording at higher sampling rates.
- Added support for flexible buffer size to allow upto 4096 bytes.

Bug: 7223456
Change-Id: Ic0522d92de905b04481a0d8daa103c77552257e8
Signed-off-by: Iliyan Malchev <malchev@google.com>