twl4030-core cleanup

twl4030-core cleanup

A variety of twl4030-core cleanups:

 - SIH register declarations moved from core.c to twl4030.h, for
   keypad, madc, bci; this decouples from twl4030-madc.h; add
   several omitted register decls; remove a duplicate.

 - Use a global "inuse" flag, not a per-slave one;

 - Remove pointless SLAVENUM_NUM symbols; just use 0/1/2/3

 - Comments:
     * Add comments:  header, register values
     * Add some section delimiters
     * Correct clock init and other comments

 - Minor stuff:
     * Group some variables and code with sibling
     * Make clock init a bit simpler
     * List twl5030 in supported i2c chips list
     * Remove needless "return;"

And one IRQ-related bugfix:  if the I2C timeout bug strikes while
reading PIH interrupt status, force an immediate retry.  Otherwise
the twl4030 IRQ will never get re-enabled...

Object size shrinks by 180 bytes, w00t!

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