davinci: DA850/OMAP-L138 EVM: add support for TPS65070 PMIC

This patch adds support for using the TPS65070 PMIC found
on the DA850/OMAP-L138 EVM.

It defines the power rail consumer mapping and registers the
the I2C based PMIC as a board device.

The power rail constraints are derived from the maxmimum and
minimum recommended operating condition values of the respective
consumers derived from section 5.2 of the OMAP-L138 datasheet.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>