mangopi-mq-pro: few fixes and improvement

This mr bring those fixes and improvement :

1.mangopi-mq-pro: fix wrong uboot offset

2.mangopi-mq-pro: remove unnecessary uboot-script.cmd by moving grub's efi file to correct path

3.mangopi-mq-pro: use generated grub.cfg

4.u-boot-mangopi-mq-pro:fix the wrong url

The uboot offset is wrong in mangopi-mq-pro because i didnt test it properly when i was making the !3761 (merged).

Also the url of u-boot-mangopi-mq-pro is wrong because i didnt change my typo properly when i was making the !3761 (merged).

Sorry for the inconvenience.

Related Issue : #1898