Check size of the firmware image parts

Prevent building unbootable firmware images.

Resolves: openbmc/openbmc#3314

Tested: I checked builds for `palmetto` and `romulus`.
To reproduce the problem I appended a big file to initramfs by modify
`meta-phosphor/common/recipes-phosphor/initfs/obmc-phosphor-initfs.bb`.
The building process failed with message about too large initramfs image.

Change-Id: I0176e9c47a9cb26ce8ba588794e681b6426d567d
Signed-off-by: Alexander Filippov <a.filippov@yadro.com>