rom loader: fix sparc -kernel boot.

rom loader: fix sparc -kernel boot.

Changes:
(1) register pstrcpy_targphys() in rom list, it is used for kernel
command lines by a number of architectures.
(2) add rom_ptr() function to get a pointer for applying changes
to loaded images.  Needed for example to tell the linux kernel
where it finds the initrd image by updating the header.
(3) make sparc use rom_ptr for initrd setup.

booting sparc-test works now, and 'info roms' shows this:

(qemu) info roms
addr=0000000000000000 size=0x2a3828 mem=ram name="phdr #0: vmlinux-2.6.11+tcx"
addr=00000000007ff000 size=0x00000e mem=ram name="cmdline"
addr=0000000000800000 size=0x400000 mem=ram name="/root/qemu-test/sparc-test/linux.img"
addr=0000000070000000 size=0x0e4000 mem=rom name="phdr #0: /home/kraxel/projects/qemu/build-zfull/pc-bios/openbios-sparc32"

reboot via 'system_reset' works too.

Patchworks-ID: 35262
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>