package/freescale-imx/firmware-imx: fix sdma/vpu firmware install path

package/freescale-imx/firmware-imx: fix sdma/vpu firmware install path

In a patch set that did not get in for other reasons, Sebastien proposed
to fix the install path directory of the sdma and vpu firmware code [1]:

	"Mainline and NXP kernels expect the sdma firmware to be in
	/lib/firmware/imx/sdma so fix the install path [...]"

By looking at the code, I believe this is correct even though I have no
means to test it.

[1] http://lists.busybox.net/pipermail/buildroot/2020-June/284875.html

Suggested-by: Sébastien Szymanski <sebastien.szymanski at armadeus.com>
Signed-off-by: Stephane Viau <stephane.viau@oss.nxp.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>