nitro_enclaves: Merge contiguous physical memory regions

nitro_enclaves: Merge contiguous physical memory regions

There can be cases when there are more memory regions that need to be
set for an enclave than the maximum supported number of memory regions
per enclave. One example can be when the memory regions are backed by 2
MiB hugepages (the minimum supported hugepage size).

Let's merge the adjacent regions if they are physically contiguous. This
way the final number of memory regions is less than before merging and
could potentially avoid reaching maximum.

Reviewed-by: Andra Paraschiv <andraprs@amazon.com>
Signed-off-by: Longpeng <longpeng2@huawei.com>
Link: https://lore.kernel.org/r/20211107140918.2106-2-longpeng2@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>