Fix loading of ELF multiboot kernels

Fix loading of ELF multiboot kernels

The multiboot implementation assumed that there is only one program header
(which contains the entry point) and that the entry point is at the start of
the code. This doesn't hold true generally and caused too little data to be
loaded.

Fix the loading code to pass the whole loaded data to the Multiboot Option ROM.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
(cherry picked from commit 092493be3caab1ac77f4223b4c3fb0975d1ed490)