scripts/checkdeps: add dependency 'bc', needed for building the kernel, see https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=70730bca1331fc50c3caacaea00439de1325bd6e

Signed-off-by: Stephan Raue <stephan@openelec.tv>
xbmc: add PR2890

Signed-off-by: Stephan Raue <stephan@openelec.tv>