[CORE] Simplify vmm_host_memunmap() and vmm_host_iounmap() APIs

Generally in unix-like OSes (such as Linux, Free BSD, Net BSD, etc.)
the memory/io unmap functions don't require size parameter. It is
also a bit odd/non-standard to expect size parameter in these functions.

This patch removes the need of size parameter in vmm_host_memunmap()
and vmm_host_iounmap() APIs.

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