init-install-efi.sh: fix to handle the boot partition correctly

init-install-efi.sh: fix to handle the boot partition correctly

(This patch was originally done against init-install.sh in
OE-Core rev aa67b1333b4774e1845f562085f7048df65a644f)

Previously, the boot partition was created for the target hard drive
but there was no corresponding entry for it in /etc/fstab. Besides,
even if the boot partition was mounted, it would just result in odd
directory hierarchy like /boot/boot/grub. However, what we really need
is /boot/grub. This patch fixes this problem.

Besides, for future maintance work, this patch also renames some of the
intermediate directories. It uses more descriptive names like /tgt_root
and /src_root. The name of /ssd is dropped.

(From OE-Core rev: 3b1bae7ad8d36930aae840175c6a3433c1469772)

Signed-off-by: Drew Moseley <drew_moseley@mentor.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>