tegra3-common: Fix low audio volume when recording videos

The Camera likes to use the back mic which does not work as intended.
Remove it from the audio_policy.conf so that the normal mic is used.

Change-Id: I5b7657f9899c02713ff44dff78b4da5bd912297d
tegra3-common: sysfs_devices_system_cpu is now in the central policy

Change-Id: Ia28cd46086a2acaf20a6e17ac0b5dc52471e6272