memblock, nobootmem: add memblock_virt_alloc_low()

memblock, nobootmem: add memblock_virt_alloc_low()

The new memblock_virt APIs are used to replaced old bootmem API.

We need to allocate page below 4G for swiotlb.

That should fix regression on Andrew's system that is using swiotlb.

Signed-off-by: Yinghai Lu <[email protected]>
Cc: Russell King <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Acked-by: Santosh Shilimkar <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>