[Qemu-ppc] private handlers to reload images when virtual machine reset.

[Olivia Yin]

This is the first part of the patches which remove rom related functions in 
loader.c The second part will optimize memory regions which use rom_ptr.

These patches are against the master branch of git://git.qemu.org/qemu.git.

The v2 patches had been updated to replace tar_target_phys_addr_t with hwaddr.