imx: caam: new u-boot command to set PRIBLOB bitfield from CAAM SCFGR register to 0x3

It is highly recommended to set the PRIBLOB bitfield to 0x3 once your
encrypted boot image has booted up, this prevents the generation of new
blobs that can be used to decrypt an encrypted boot image. The PRIBLOB is
a sticky type bit and cannot be changed until the next power on reset.

Add the set_priblob_bitfield U-Boot command to prevent the generation of
new blobs.

Signed-off-by: Clement Le Marquis <clement.lemarquis@nxp.com>
Acked-by: Ye Li <Ye.Li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>