ft2232_spi: reintroduce generic GPIOL control

This reintroduces a reworked version of the GPIOL pin control first
introduced in commit 3207844 (CB:49637), which was reverted in commit
6518cf3 (CB:55692) due to breakage.

This change introduces a new argument `gpiolX` to allow use of the four
GPIOL pins either as generic gpios or as additional CS# signal(s). `X`
specifies the GPIOL pin (0-3) to be set to one of [HLC] with the
following meaning:

 * H - set the pin as output high
 * L - set the pin as output low
 * C - use the pin as additional CS# signal

The third value, `C`, aims to replace the parameter `csgpiol`, that is
now marked as deprecated and can be removed at some point in the future.
`gpiol` and `csgpiol` are mutually exclusive and use of both results in
an error.

Multiple pins may be set by specifying the parameter multiple times.

Documentation was updated/added accordingly.

Test: All pin levels/modes have been verified to behave correctly with a
      logic analyzer.

Change-Id: I3989f0f9596c090de52dca67183b1363dae59d3a
Signed-off-by: Alan Green <avg@google.com>
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
---
M flashrom.8.tmpl
M ft2232_spi.c
2 files changed, 109 insertions(+), 9 deletions(-)