x86: zImage: Move subarch assignment out of cmd_line check

x86: zImage: Move subarch assignment out of cmd_line check

The commit

  20bfac0599bd ("x86: zImage: add Intel MID platforms support")

introduced an assignment of subarch field in boot parameters, though
missed the right place of doing that. It doesn't matter if we have or
not a kernel command line supplied, we just set that field. Although
guard it by protocol version which supports it.

Fixes: 20bfac0599bd ("x86: zImage: add Intel MID platforms support")
Cc: Vincent Tinelli <[email protected]>
Signed-off-by: Andy Shevchenko <[email protected]>
Reviewed-by: Bin Meng <[email protected]>