xen/arm: Harden setup_frametable_mappings

xen/arm: Harden setup_frametable_mappings

The amount of supported physical memory depends on the frametable size
and the number of struct page_info entries that can fit into it. Define
a macro PAGE_INFO_SIZE to store the current size of the struct page_info
(i.e. 56B for arm64 and 32B for arm32) and add a sanity check in
setup_frametable_mappings to be notified whenever the size of the
structure changes. Also call a panic if the calculated frametable_size
exceeds the limit defined by FRAMETABLE_SIZE macro.

Update the comments regarding the frametable in asm/config.h.

Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>