kvmvapic: align start address as well as size

kvmvapic: align start address as well as size

The kvmvapic code remaps a section of ROM as RAM to allow the guest to
maintain state there.  It is careful to align the section size to a page
boundary, to avoid creating subpages, but neglects to do the same for
the start address.  These leads to an assert later on when the memory
core tries to create a page which is half RAM and half ROM.

Fix by aligning the start address to a page boundary.

This can be triggered by running qemu-system-x86_64 -enable-kvm -vga none.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>