memory.lua: dma_alloc() now returns physical address as a Lua number.

This "should be OK" provided that physical addresses fit in 52 bits of
precision which I think they do on machines with less than petabytes
of memory. (Certainly not the last word on this topic....)
intel.lua: Use memory.dma_alloc() instead of C.map_physical_ram.

Hurray! Snabb Switch now runs on a standard Linux with no special boot
parameters. You can retire your "memmap=..." grub lines.