xen: portability clean up and some minor clean up for xencomm.c
xen: portability clean up and some minor clean up for xencomm.c

clean up of xencomm.c. is_phys_contiguous() is arch dependent
function that depends on how virtual memory are laid out.
So split out the function into arch specific code.

Signed-off-by: Isaku Yamahata <4b3abd66323411eeceff090ab3754dd766fc4b25@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <35cfe9f678a9e9bbdcf2f6e68cd105ce06d149b1@citrix.com>
Cc: Isaku Yamahata <4b3abd66323411eeceff090ab3754dd766fc4b25@valinux.co.jp>
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@elte.hu>
Cc: "Luck, Tony" <e7984595ec0368ff920a7b3521dc7093683f6f26@intel.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas