feat(xCAT-server): reserve a crash kernel for riscv64 diskless images

The kdump branch of the diskless kernel command line has a default
reservation for ppc64 and x86 only. On any other architecture an image
with linuximage.dump set but no linuximage.crashkernelsize got dump= and
no crashkernel= at all, so the kernel reserved nothing and kdump could
never run. EL has no default reservation for riscv64 either
(kdumpctl get-default-crashkernel is empty there), so nothing else fills
the gap.

Give riscv64 the same treatment as the architectures around it and
default to 256M. An explicit crashkernelsize still wins, and images
without dump are unchanged.

xCAT-server/lib/xcat/plugins/anaconda.pm

@@ -918,6 +918,11 @@ sub mknetboot
                 if ($arch =~ /86/) {
                     $kcmdline .= " crashkernel=128M dump=$dump ";
                 }
+                if ($arch eq "riscv64") {
+                    # EL has no default reservation for riscv64, so without an explicit
+                    # linuximage.crashkernelsize the kernel would reserve nothing at all
+                    $kcmdline .= " crashkernel=256M dump=$dump ";
+                }
             }
         }