dma: Rename xilinx dmatest to axidmatest

dma: Rename xilinx dmatest to axidmatest

The reason is that there is standard dmatest in dma folder
a because of the design of these xilinx proprietary tests
without binding that ends in duplicating filenames
just because of the same driver name.

Warning log:
WARNING: at fs/sysfs/dir.c:536 sysfs_add_one+0x78/0x98()
sysfs: cannot create duplicate filename '/module/dmatest/parameters/iterations'

Renaming driver to different name caused that kernel
will use different module name.

~ # ls /sys/module/ | grep dma
axidmatest
cdmatest
dmatest
vdmatest

Signed-off-by: Michal Simek <michal.simek@xilinx.com>