pc-bios: add missing riscv64 descriptor

pc-bios: add missing riscv64 descriptor

Without descriptor libvirt cannot discover the EDK II binaries via
the qemu:///system connection.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Message-ID: <20241212090059.94167-1-heinrich.schuchardt@canonical.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 74dc38d0c6c15fd57a5dee94125d13ac5b00491d)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: context fix in pc-bios/descriptors/meson.build due to missing
 v9.1.0-337-gb883fb93db "roms: Support compile the efi bios for loongarch")