ata: mvebu: move mvebu sata driver to drivers/ata directory

Currently mvebu sata driver is in arch/arm/mach_mvebu directory, this
patch moves it to drivers/ata directory with renaming "sata.c" to
"ahci_mvebu.c" which is aligned to Linux.
New ahci driver's kconfig option is added as AHCI_MVEBU which selects
SCSI_AHCI and is based on AHCI.

Signed-off-by: Ken Ma <make@marvell.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Stefan Roese <sr@denx.de>