Allow a device to define the max number of service groups in init.h

Certain proprieatary binaries (such as tcmd for instance) require
more than 12 supplementary service groups.  By definiing:
TARGET_NR_SVC_SUPP_GIDS := in BoardConfig this can now be changed
per device.

Change-Id: I8f968adc21768ca90232ded7b7e1ffa68dc7ea78