gallium/radeon: link in libradeon.la at target level

gallium/radeon: link in libradeon.la at target level

It makes more sense to link the core and common parts of the driver as the
target is build. Additionally this will help us drop duplicating symbols
for targets that static link mulitple pipe-drivers. Only egl-static needs
that currently with more to come.

To simplify things a bit add HAVE_GALLIUM_RADEON_COMMON variable.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>