arm64: dma-mapping: alloc page order based on domain pgsize

Restrict higher-order allocation to pgsize preferce per domain and avoid
wasting any time or effort on other sizes which offer no benefit.

Change-Id: Ic0a7843917e7c6e2959e7b566c20fec6a96670f3
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>