nios2: move command line configuration to Kconfig

This patch moves command line configuration from board header
file to board defconfig in the way of Kconfig. The change passed
savedefconfig.

This fixes warnings such as : "CONFIG_SYS_HUSH_PARSER" redefined,
when "Use hush shell" is selected with menuconfig, etc.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>