dma: mv_xor: rename mv_xor_shared_platform_data to mv_xor_platform_data

'struct mv_xor_shared_platform_data' used to be the platform_data
structure for the 'mv_xor_shared', but this driver is going to be
renamed simply 'mv_xor', so also rename its platform_data structure
accordingly.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>