* Fixed rate operation for es1370 chip to solve conflicting

* Fixed rate operation for es1370 chip to solve conflicting
  sampling rate between playback and recording. This can be
  disabled / enabled via kernel hints
  (hint.pcm.<unit>.fixed_rate=0/4000-48000) or sysctl
  hw.snd.pcm<unit>.fixed_rate=0/4000-48000). Default to 48khz
  fixed rate. [1]
* Basic cleanup. *_es1371x_* -> *_es137x_*.
* Some locking fixes. [2]

Submitted by:	Ariff Abdullah <skywizard@MyBSD.org.my>
Discussed with:	yongari [2]
See also:	http://lists.freebsd.org/pipermail/freebsd-multimedia/2005-September/002758.html [1]
Reported by:	Jos Backus <jos at catnook.com> [1]