rilmodem: probe availability of libandroid-properties

The Android telephony java framework is responsible for setting
multiple several system properties. Since Android system properties
are mostly world-wide readable, they may mean something to other
components such as rild. In some cases, rild may not function
normally without these properties being set correctly.

A detail, but might not be complete, list is available in
https://android.googlesource.com/platform/frameworks/base/+/master/telephony/java/com/android/internal/telephony/TelephonyProperties.java

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gril: use standard radio tech names

Android defines all names for valid radio technologies in
android.telephony.ServiceState.rilRadioTechnologyToString(). Just
follow it.

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gril: add PersoSubstate constants

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
Merge commit 'ab9f135194d9b0e88fad48bdc620624c768edc8d' into mx4-porting
rilmodem: set android properties if available

Supported so far:
 * gsm.network.type
 * gsm.sim.operator.iso-country
 * gsm.sim.operator.numeric
 * gsm.sim.state
 * gsm.version.baseband

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
Merge branch 'launchpad/1399106/mx4-porting/android-properties' into mx4-porting