Most of the changes are self-explanatory and just follow what's
already happening for existing architectures.
Two things are worth pointing out:
* we need to use shim-unsigned instead of shim-signed because
riscv64 is not fully integrated into Fedora yet and so we
can't do Secure Boot signing for the time being;
* we use ext4 as bootfilesystem since in most cases the
underlying firmware is going to be U-Boot, which needs to be
able to load the board's DTB from /boot and doesn't support
XFS.
Signed-off-by: David Abdurachmanov <davidlt@rivosinc.com>
