DeviceInfoUtils.java: support to show kernel version compiled with clang

The kernel version displayed in settings is only shown correctly
when built with gcc, this change adds support for a kernel built
with clang.

Test: manually on hikey with following command:
adb shell am instrument -w -e class com.android.settings.DeviceInfoSettingsTest com.android.settings.tests.unit/android.support.test.runner.AndroidJUnitRunner

Change-Id: I9b7991681cb5abdf44e7d1d1bff84c7c866be2ed
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>