[CORE] Added flags for specifying normal write-through memory

This patch adds define VMM_MEMORY_FLAGS_NORMAL_WT for specifying
flags required for a norma write-through memory.

With this patch, we have three types flags for host memory:
VMM_MEMORY_FLAGS_NORMAL -> Normal RAM  (cacheable & writeback)
VMM_MEMORY_FLAGS_NORMAL_WT -> Normal + Writethrough (cacheable & writhrough)
VMM_MEMORY_FLAGS_IO -> Device registers

Signed-off-by: Anup Patel <anup@brainfault.org>