Provide ldl_phys et al.

Provide ldl_phys et al.

We implement these in the Xen DM case as simple unoptimised wrappers
around cpu_physical_memory_write.

Several were copied directly from this qemu upstream commit:

    commit aab33094073678d459ccaac5c60ea7533e8d1d8e
    Author: bellard <bellard@c046a42c-6fe2-441c-8c8c-71466251a162>
    Date:   Sun Oct 30 20:48:42 2005 +0000

	more physical memory access functions

	git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@1587 c046a42c-6fe2-441c-8c8c-71466251a162

I handwrote the others in the same pattern.