arm: omap4: panda: Add reading of the board revision

arm: omap4: panda: Add reading of the board revision

Detect if we are running on a panda revision A1-A6,
or an ES panda board. This can be done by reading
the level of GPIOs and checking the processor revisions.
This should result in:
Panda 4430:
     GPIO171, GPIO101, GPIO182: 0 1 1 => A1-A5
     GPIO171, GPIO101, GPIO182: 1 0 1 => A6
Panda ES:
     GPIO2, GPIO3, GPIO171, GPIO48, GPIO182: 0 0 0 1 1 => B1/B2
     GPIO2, GPIO3, GPIO171, GPIO48, GPIO182: 0 0 1 1 1 => B3

Set the board name appropriately for the board revision that
is detected.

Update the findfdt macro to load the a4 device tree binary.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
[trini: %s/CONTROL_PADCONF_CORE/(*ctrl)->control_padconf_core_base/ and
 formatting for that]
Signed-off-by: Tom Rini <trini@ti.com>