[GRUB] Use Seco's GRUB repository and add sysdata & bootscript support
Instead of using the default GRUB2.12 source code extracted from a tarball, now the source code is gathered from SECO's GRUB repository: https://git.seco.com/clea-os/bsp/intel/grub2-seco
The customized SECO's GRUB supports sysdata as a module (compiled as built-in).
Add bootscript for GRUB bootloader following the implementation of the bootscript for U-boot.
JIRA Reference: [CLEAOS-648, CLEAOS-673]
Signed-off-by: Nicola Sparnacci nicola.sparnacci@seco.com