drivers/dma: make mv_xor.c driver explicitly non-modular

The Kconfig for this driver is currently:

config MV_XOR
        bool "Marvell XOR engine support"

...meaning that it currently is not being built as a module by anyone.
Lets remove the modular code that is essentially orphaned, so that
when reading the driver there is no doubt it is builtin-only.

Since module_init translates to device_initcall in the non-modular
case, the init ordering remains unchanged with this commit.

We leave some tags like MODULE_AUTHOR for documentation purposes.
Also note that MODULE_DEVICE_TABLE is a no-op for non-modular code.

Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: dmaengine@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>