android: adapt to the megadriver mechanism

android: adapt to the megadriver mechanism

Fixes linker error:
  ld:
  .../libmesa_dri_common_intermediates/libmesa_dri_common.a(dri_util.o):
    in function globalDriverAPI:dri_util.c(.data.rel+0x0): error:
    undefined reference to 'driDriverAPI'

As an example, you can see that mesa_dri_drivers
also uses common/libmegadriver_stub (src/mesa/drivers/dri/Makefile.am)

The _stub part might be confusing, but
it actually provides the dri-driver shared lib constructor,
megadriver_stub_init, which will later on load the real
platform dependent part and call
l __driDriverGetExtensions_<platform>

Cc: "10.1 10.2" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Adrian Negreanu <adrian.m.negreanu@intel.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>