pollux-common: use hdpi instead of xlarge

fixes build error trying (parsing xlarge resources)

analog to https://github.com/CyanogenMod/android_device_sony_castor_windy/commit/0a704d218a45c43d0fff163a5fe806d688d1a237

Change-Id: I17a1b2c28f25a0b847b49df295548f9ff93a1982