Revert "mxgrub: Change crashkernel size to 512MB"

This reverts commit 8b85866.

With nr_cpus=1 256M is enough even for kraios.

mxgrub/mxgrub

@@ -239,7 +239,7 @@ sub scan_mariux {
 	}
 }
 
-our $KERNEL_PARAMETER="ro crashkernel=512M console=ttyS1,115200n8 console=tty0 init=/bin/systemd audit=0";
+our $KERNEL_PARAMETER="ro crashkernel=256M console=ttyS1,115200n8 console=tty0 init=/bin/systemd audit=0";
 
 sub update_grub_cfg {
 	my $kernellist='';