Rename SDIMG_PART1_SIZE_MB to SDIMG_BOOT_PART_SIZE_MB.
Rename SDIMG_PART1_SIZE_MB to SDIMG_BOOT_PART_SIZE_MB.

Partition 1 is an implementation detail, the important thing is that
it is the boot partition.

Signed-off-by: Kristian Amlie <505e66ae45028a0596c853559221f0b72c1cee21@mender.io>

GregorioDiStefano/meta-mender,bboozzoo/meta-mender,bboozzoo/meta-mender,bboozzoo/meta-mender,GregorioDiStefano/meta-mender,GregorioDiStefano/meta-mender,bboozzoo/meta-mender