sound: wcd9304: add CONFIG_SND_SOC_WCD9304_SWITCH_PORT in wcd9304

* In stock audio, HTC uses a sound config flag named
  "CONFIG_SND_SOC_WCD9304_SWITCH_PORT". This effectively re-arranges
  the TX1/TX2 channels to TX3/TX4. Implement it into wcd9304.c

* Add CONFIG_SND_SOC_WCD9304_SWITCH_PORT=y to m4_defconfig.

* Have HTC m4 Kconfig select it regardless of defconfig to ensure
  TX audio is enabled.

Change-Id: I89129206dd57b26f0b6644131bf6c6bae4a6cfd7