ft2232_spi.c: Add ft2232_spi_send_multicommand()

Pack WREN and op in one ftdi_write_data() call.
Pack RD cmd and deassertion of CS# in one ftdi_write_data() call.

Every ftdi_write_data() call is quite time consuming as the ftdi-chips
seems to take always 2-3ms to respond.
This leads to what the comment already says: Minimize USB transfers
to ftdi chip by packing as many commands as possible together.

So I packed the WREN command together with the following operation
which can be program or erase operation.
Furthermore the deassertion of CS# is no longer send seperately
from a read cmd.

This saves more than 1 minute when programming a 128MBit Flash
with my config!

Signed-off-by: Simon Buhrow <simon.buhrow@posteo.de>
Change-Id: Ie4a07499ec5ef0af23818593f45dc427285a9e8a
---
M ft2232_spi.c
1 file changed, 91 insertions(+), 1 deletion(-)