This commit implements functions icjx_multireadpin and icjx_multiwritepin.
These functions can be used for multiple pin access (read/write) if
CONFIG_IOEXPANDER_MULTIPIN is selected. This access is generally
faster than one by one pin and may simplify user application.
Changes to general functions icjx_read and icjx_write were also required
to provide support for multiple data send/receive.
Signed-off-by: Michal Lenc <michallenc@seznam.cz>