spapr: Use address from elf parser for kernel address

spapr: Use address from elf parser for kernel address

tl;dr: This allows Big Endian zImage booting via -kernel + x-vof=on.

QEMU loads the kernel at 0x400000 by default which works most of
the time as Linux kernels are relocatable, 64bit and compiled with "-pie"
(position independent code). This works for a little endian zImage too.

However a big endian zImage is compiled without -pie, is 32bit, linked to
0x4000000 so current QEMU ends up loading it at
0x4400000 but keeps spapr->kernel_addr unchanged so booting fails.

This uses the kernel address returned from load_elf().
If the default kernel_addr is used, there is no change in behavior (as
translate_kernel_address() takes care of this), which is:
LE/BE vmlinux and LE zImage boot, BE zImage does not.
If the VM created with "-machine kernel-addr=0,x-vof=on", then QEMU
prints a warning and BE zImage boots.

Note #1: SLOF (x-vof=off) still cannot boot a big endian zImage as
SLOF enables MSR_SF for everything loaded by QEMU and this leads to early
crash of 32bit zImage.

Note #2: BE/LE vmlinux images set MSR_SF in early boot so these just work;
a LE zImage restores MSR_SF after every CI call and we are lucky enough
not to crash before the first CI call.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Tested-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Message-Id: <20220504065536.3534488-1-aik@ozlabs.ru>
[danielhb: use PRIx64 instead of lx in warn_report]
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>