xen/types: Correct the definition of uintptr_t

xen/types: Correct the definition of uintptr_t

uintptr_t is specified as unsigned int in 32bit, not unsigned long.  This is
why, when copying inttypes.h from GCC, the use of PRIxPTR and similar is
broken for 32bit builds.

Use __attribute__((__mode__(__pointer__))) to get the compilers default
pointer type, which matches the pre-existing inttypes.h

Fix the identified breakage with ELF_PRPTRVAL

Compile tested on all architectures, with a manual printk() to trigger any
potential -Wformat issues.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>