A collection of fixes to Xen common files

A collection of fixes to Xen common files

- call free_xenoprof_pages only ifdef CONFIG_XENOPROF;
- define PRI_stime as PRId64 in an header file;
- respect boundaries in is_kernel_*;
- implement is_kernel_rodata;
- guest_physmap_add_page should be ((void)0).
- fix guest_physmap_add_page;
- introduce CONFIG_XENOPROF;
- define _srodata and _erodata as const char*.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>
Committed-by: Keir Fraser <keir@xen.org>