imx-lib: bump to version 5.1

imx-lib: bump to version 5.1

Change version to be independent of BSP version.  This limits
confusion on future BSP updates that do not include imx-lib updates.

Changelog since 3.14.28-1.0.0_ga:
- Add i.MX 7D support.
- Change LICENSE file.
- Enable pxp libraries for i.MX 6UltraLite.
- Fix rng and shara2 to exclude the 6UL platform to avoid build breaks

This patch is based on the Yocto equivalent:
https://github.com/Freescale/meta-fsl-arm/commit/b299454
https://github.com/Freescale/meta-fsl-arm/commit/5f28af0

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