ugps: add quality measurement parameters

ugps: add quality measurement parameters

The current version of ugps does not report any quality parameters for
GPS receiver fixation. Considering the positioning error, which can be
up to hundreds of meters, it is helpful to know how accurately the GPS
determines the position.

This PR supports determining the number of satellites and the HDOP
(Horizontal Dilution of Precision) parameter to address this.  The GPGGA
sentence is already parsed in the code, so it just extends the amount of
data it reads.

Fixes: #2 (ugps miss GPS quality parameters)
Signed-off-by: Zbynek Kocur <zbynek.kocur@fel.cvut.cz>
Signed-off-by: Petr Štetiar <ynezz@true.cz> [whitespace fixes, long line wrap]