ARM: OMAP1: ams-delta: add GPIO lookup tables

Scope of the change is limited to GPIO pins used by board specific
device drivers which will be updated by follow-up patches of the
series. Those are some OMAP GPIO (gpio-0-15) and most of Amstrad Delta
latch2 GPIO bank pins. Remaining pins of those banks, as well as
Amstrad Delta latch1 pins, will be addressed later.

Assign a label ("latch2") to the bank, enumerate its pins and put that
information, together with OMAP GPIO bank pins, in GPIO lookup tables.
Assign lookup tables to devices as soon as those devices are registered
and their names can be obtained.

A step froward in:
- removal of hard-coded GPIO numbers from drivers,
- removal of board mach includes from drivers,
- switching to dynamically assigned GPIO numbers.

Created and compile tested agains linux-4.17-rc3

Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>