[CORE] devemu: Add APIs to emulate read/write over guest IO space

Architectures such as x86 and PowerPC access devices via memory space
or IO space hence for guest on these architectures we would require
separate APIs for emulating device read/write over IO space.

This patch adds APIs to emulate virtual read/write over guest IO
space.

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