x86: galileo: Fix boot failure

With latest codes on mainstream master, Intel Galileo board does not
boot unfortunately. Git biset leads to b383d6c0 "bootstage: Convert
to use malloc()".

Disable bootstage support to make it boot again. The root cause needs
to be investigated however.

Fixes: b383d6c0 ("bootstage: Convert to use malloc()")
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>