ft2232_spi.c: release I/Os on shutdown

Resets FTDI I/O pins to high-Z (input) when shutting down. This allows
other devices to use the SPI bus without having to disconnect the
programmer.

This change will introduce a backward incompatibility in the case where
a user is relying on the state of FTDI outputs post-programming (eg. to
disallow another device from driving CS low).

However, there are likely more cases where releasing the SPI bus is the
correct thing to do.

Signed-off-by: Alan Green <avg@google.com>
Change-Id: I9fae55e532595752983f55fac2298f81699dbe5b
---
M ft2232_spi.c
1 file changed, 26 insertions(+), 0 deletions(-)