ion: ion_system_heap: update supported page-orders for ion pool

The supported mappings for ARMv8 are 1GB, 2MB, 64KB and 4KB. So 1MB
allocations from ion pool is not used for ARMv8 section map. Such
allocations end up being mapped as multiple 64K sections map, while still
using 1MB contiguous memory. In case of ARMv7s, page-order 9 allocations
are not used as section map.

Drop page-order 8 ion pool for builds using ARMv8 pagetables and page-order
9 ion pool for builds using ARMv7s.

Change-Id: Ifff2d8f1cf61ce443311d16c11b8edc191b27a22
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>