Add support for TCA6424A

This patch extends the PCA953x driver to support TI's TCA6424A 24 bit I2C I/O expander. The patch is based on code by Michele
Bevilacqua.

Changes in v2:
- Compare ngpio against 24 in both places, not >16
- Larger datatype now u32 instead of uint.
  Bit fields not used for struct members since their address is taken.
- Be precise: TCA6424A (untested for older TCA6424)

Signed-off-by: Andreas <Schallenberg&lt;Andreas.Schallenberg@3alitytechnica.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>