libsensors: Added support for Pressure sensor

libsensors: Added support for Pressure sensor

This patch adds the HAL specific changes for Pressure Sensor.
This uses IIO model to communicate to kernel driver.
This exposes pressure data in hPa format.

Change-Id: I7242be355885a0860de0fb496de800bc7b212ca3
Signed-off-by: Archana Patni <archana.patni@intel.com>
Reviewed-on: https://android.intel.com/162268
Reviewed-by: Persson, Per <per.persson@intel.com>
Reviewed-by: Sesha, Subramony <subramony.sesha@intel.com>
Tested-by: sys_abtbuild <sys_abtbuild@intel.com>
Reviewed-by: Lilja, Ola <ola.lilja@intel.com>