uboot_api: fix loglevels
uboot_api: use _dputc instead of uart_putc and use uart_tstc only if UART is enabled
uboot_api: storage: fix detection of multiple devices of the same type
lib: tar: add simple tar library which can find a file and copy it into a buffer
app: aboot: support loading grub from a tar archive
msm8960: enable libtar
uboot_api: part: add virtual mmc device which represents the tar archive where we store GRUB
uboot_api: tell GRUB from which device we booted it from