package/freescale-imx/imx-gpu-viv: move pkg-config files fixup to the build step

package/freescale-imx/imx-gpu-viv: move pkg-config files fixup to the build step

The fixup of the pkg-config files modifies files in the build
directory (@D) but is done in the staging installation step, which
doesn't make much sense, especially since the build step already has
some fixup logic. So we move the fixup logic of the pkg-config files
into the build step.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>