debian: fix grub package arch selectors for riscv64

grub-efi-amd64-bin used [!arm64] which incorrectly pulls amd64 grub on
riscv64 hosts. Change to explicit [amd64] selector and add
grub-efi-riscv64-bin [riscv64].

Author: monkey-jsun

base/debian/control

@@ -40,7 +40,8 @@ Depends: adduser,
          dnsmasq-base,
          ebtables-legacy | ebtables,
          grub-efi-arm64-bin [arm64],
-         grub-efi-amd64-bin [!arm64],
+         grub-efi-amd64-bin [amd64],
+         grub-efi-riscv64-bin [riscv64],
          iproute2,
          iptables,
          libarchive-tools | bsdtar,