Hello Laacid, thanks for joining the Intel Community.
UEFI shell can be enabled on BIOS in the boot options menu. Bear in mind that this doesn't boot the shell, but enables UEFI boot in general.
We do not have the commands or the efi shell binaries you need to use, therefore I would recommend you to get in touch with the LSI so they can let you know what you need to flash the Raid card.
Thanks very much. I did the following to get to a shell so I could flash the card:
Get a USB drive
Use USBwriter to create bootable USB drive with archlinux ISO
Add files if you need them to the USB drive for flashing purposes
Set your motherboard to boot UEFI devices (possibly disable secureboot)
Boot and select proper UEFI version- either v1 or v2. I just did trial and error to find the right one- v1 for me
consult your card's website for flashing instructions and updates needed.