Android: fix r300g only build

Android: fix r300g only build

If r300g is the only radeon driver built, the Android build fails to
build:

ninja: error:
'out/target/product/linaro_x86_64/obj/STATIC_LIBRARIES/libmesa_pipe_radeon_intermediates/export_includes',
needed by
'out/target/product/linaro_x86_64/obj/SHARED_LIBRARIES/gallium_dri_intermediates/import_includes',
missing and no known rule to make it

This is because the path to build libmesa_pipe_radeon was only getting
added for r600g and radeonsi, but the library dependency was added for
all radeon drivers. As libmesa_pipe_radeon is not needed for r300g, drop
the library dependency.

Cc: Mauro Rossi <issor.oruam@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Emil Velikov <emil.velikov@collabora.com>