Q35: implement property interfece to several parameters

During creation of Q35 instance several parameters are set using direct access.
It violates Qemu device model. Correctly, the parameters should be handled as
object properties.

The patch adds four link type properties for fields:
mch.ram_memory
mch.pci_address_space
mch.system_memory
mch.address_space_io
And, it adds two size type properties for fields:
mch.below_4g_mem_size
mch.above_4g_mem_size

Signed-off-by: Efimov Vasily <real@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>