x86: remove virt_to_bus in pci-dma_64.c

virt_to_bus() is deprecated according to the docs, and moreover,
won't return the right thing in i386 if we're dealing with high memory mappings.
So we make our allocation function return a page, and then use page_address() (for
virtual addr) and page_to_phys() (for physical addr) instead.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>