SamsungExynos4RIL: fix signal strength

Doesn't work with Gingerbread radios!

Since ICS, the modem sends the signal strength in the first 8 bits
and the number of bars as from bit 9.
For old radios the first 8 bits are always 99.

Change-Id: I67b31baf18cbce2dfa7e6f8b096caaae74cd7cd8
Merge "SamsungExynos4RIL: fix signal strength" into cm-10.1
SamsungExynos4RIL: Allow signal strength to be handled for GB modems

For devices that have no modems that support the ICS signal strength handling, allow handling it the old way with the ro.ril.gbmodem system property.

Change-Id: I68270c5a4026b2c8f448125607ee47dd04249176