memstick: factor out transfer initiating functionality in mspro_block.c

Apart from currently used standard memstick data transfer method, Sony
introduced several newer ones, to uncover full bandwidth/capacity of its
Pro, HG and XC media formats. This patch lays a foundation to enable
those methods as made possible by host/media capabilities.

As a side effect of this patch, mspro_block_read_attributes became more
streamlined and readable.

[akpm@linux-foundation.org: fix printk warning]
Signed-off-by: Alex Dubov <oakad@yahoo.com>
Reported-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>