[msm] Generate emmc_appsboot.mbn in addition to EMMCBOOT.MBN

Modem builds for different targets are in process of changing naming
from emmc_appsboot.mbn to EMMCBOOT.MBN.  Generating both images
until transition to EMMCBOOT.MBN is complete for emmc boot targets.

Change-Id: I903cdd3457c7bd31f1cfa71bee18e33fd67b6d85
4 files changed