AndroidBoot: Cleanup AndroidBoot makefile

TARGET_EMMC_BOOTLOADER and TARGET_ABL are both dependent on each other
creating a circular dependency instead use only one TARGET for
bootloader. Set SIGNED_KERNEL if verified boot is enabled instead of
TARGET_BOOTIMG_SIGNED flag which is deprecated.

Change-Id: Ica3e62b9a781050f992a6e9db78ba51fd918ecd3
1 file changed