x86: fix pinned cache attribute handling

x86: fix pinned cache attribute handling

- make sure UC- is only used for PAT purposes (MTRRs and hence EPT
  don't have this type)
- add order input to "get", and properly handle conflict case (forcing
  an EPT page split)
- properly detect (and refuse) overlaps during "set"
- properly use RCU constructs
- support deleting ranges through a special type input to "set"
- set ignore-PAT flag in epte_get_entry_emt() when "get" succeeds
- set "get" output to ~0 (invalid) rather than 0 (UC) on error (the
  caller shouldn't be looking at it anyway)
- move struct hvm_mem_pinned_cacheattr_range from header to C file
  (used only there)

Note that the code (before and after this change) implies the GFN
ranges passed to the hypercall to be inclusive, which is in contrast
to the sole current user in qemu (all variants). It is not clear to me
at which layer (qemu, libxc, hypervisor) this would best be fixed.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Acked-by: Kevin Tian <kevin.tian@intel.com>