twl4030-gpio.h removal

The <linux/i2c/...> directory has too many headers for twl4030
support.  Start simplifying that by moving twl430-gpio.h into
the main twl4030.h and also:

 - Providing comments to summarize the { module, offset } logical
   addressing vs the { i2c_client, register } physical addressing.

 - Moving the { module, offset } based I/O calls next to the place
   those modules are defined, with slightly improved descriptions.

 - Adding some section markers internal to twl4030.h so unrelated
   things can be visually separated.

 - Move TWL4030_GPIO_MAX adjacent to the other GPIO symbols.

 - Remove two more now-obsolete symbols (for GPIO pullup/pulldown).

 - Have global definitions of the three SIH_CTRL register bits,
   following the pattern of twl4030-core.c (and fixing a minor
   fault handling bug in reading the clear-on-read bit).

To keep things simple, the only blocks with register declarations
in this file should be ones with registers that (cleanly) get
shared between components ... modules with SIH registers (for
IRQ handling) being the obvious candidates.

No functional changes.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>