mesa: Replace imx with kmsro and vc4 in GALLIUMDRIVERS

mesa: Replace imx with kmsro and vc4 in GALLIUMDRIVERS

mesa 19.0.0 remove imx from gallium drivers and add kmsro, vc4 is
a kmsro dependency, so we need to enable too.

mesa commit 41a0acd6a149ec9f47ea527ad08a2b29bf1ee6b2

Author: Rob Herring <robh@kernel.org>
Date:   Thu Jan 24 14:03:54 2019 -0600

    Switch imx to kmsro and remove the imx winsys

    The kmsro winsys is equivalent to the imx winsys, so we can switch
    to it and remove the imx one.

Signed-off-by: Fabio Berton <fabio.berton@ossystems.com.br>