cmd: qfw: do not require default macros when building qfw command

The qfw command interface makes use of CONFIG_LOADADDR and
CONFIG_RAMDISKADDR to setup kernel. But not all boards have these macros,
which causes build problem on those platforms.

This patch fixes this issue.

Signed-off-by: Miao Yan <yanmiaobest@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>