media: dvb_ca_en50221: Add block read/write functions

Some lower level drivers may work better when sending blocks of data
instead byte per byte. For this we need new function pointers in the
dvb_ca_en50221 protocol structure (read_data, write_data) and the protocol
needs to execute them, if they are defined.
Block data transmission is done in all states except LINKINIT.

Original code change by Ralph Metzler, modified by Jasmin Jessich and
Daniel Scheller to match Kernel code style.

Signed-off-by: Ralph Metzler <rjkm@metzlerbros.de>
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Jasmin Jessich <jasmin@anw.at>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>