bc: extend to nativesdk

bc is needed for compiling kernel modules, more specifially
whenr running `make scripts prepare'.

In linux-yocto.inc, we have bc-native in DEPENDS. But we will
need nativesdk-bc in case we compile a kernel module inside
SDK.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>