floss: Generalize PCM buffer

The PCM ring buffer currently resets its read/write pointers only
when they are equal. However, since PCM data pulled from the CRAS
server (ChromeOS audio server) may not always match the rate of
data decoded from peer devices, this approach risks buffer overflows.
To prevent this, a more general PCM buffer solution is needed.

Bug: 333359281
Tag: #floss
Test: m Bluetooth && Ran ChromeOS HFP tests and verified HFP WBS
Flag: EXEMPT floss only changes
Change-Id: I66a7d8fe9f97fea024c0f3e13e24ccc823d5d73f