cores/dma, liblitesdcard/sdcard: use 64 bits for dma base address

cores/dma, liblitesdcard/sdcard: use 64 bits for dma base address

Make the DMA base address register 64-bit wide, to cover situations
in which the physical memory being accessed is above the 4GB limit
(e.g., on 64-bit systems with more than 4GB of provisioned physical
memory).

Also update DMA reader/writer setup call sites in the bios (currently
only used by litesdcard).

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>