davinci: am18x/da850/omap-l138: use 'NOM' voltage defined in datasheet as min voltage

davinci: am18x/da850/omap-l138: use 'NOM' voltage defined in datasheet as min voltage

For each DA850 OPP, the normal ('NOM') voltage defined in the tecnical
reference manual (TRM) is actually the minimum voltage the frequency
is supported at.

The minimum ('MIN') voltage defined in TRM is meant to take care of
voltage fluctuations and the device should not be run at this voltage
for extended periods of time.

Fix the OPP definitions to define the cvdd_min as the normal voltage
defined in the datasheet.

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