wic: add sdimage-bootpart kickstart file

wic: add sdimage-bootpart kickstart file

Add kickstart for generating a SD card image that should cover most use
case scenarios. The layout is as follows:
- 16MB vfat partition that IMAGE_BOOT_FILES will be copied to, 4k
  alignment
- ext4 rootfs, 4k alignment

(From OE-Core rev: bb01a6be7b32aa675f5003a6012a60a081212e8c)

Signed-off-by: Maciej Borzecki <maciej.borzecki@open-rnd.pl>
Signed-off-by: Maciek Borzecki <maciek.borzecki@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>