ARM: omap-common: Add standard access for board description EEPROM

ARM: omap-common: Add standard access for board description EEPROM

Several TI EVMs have EEPROM that can contain board description information
such as revision, DDR definition, serial number, etc. In just about all
cases, these EEPROM are on the I2C bus and provides us the opportunity
to centralize the generic operations involved.

The on-board EEPROM on the BeagleBone Black, BeagleBone, AM335x EVM,
AM43x GP EVM, AM57xx-evm, BeagleBoard-X15 share the same format.
However, DRA-7* EVMs, OMAP4SDP use a modified format.

We hence introduce logic which is generic between these platforms
without enforcing any specific format. This allows the boards to use the
relevant format for operations that they might choose.

This module will compile for all TI SoC based boards when
CONFIG_TI_I2C_BOARD_DETECT is enabled to have optimal build times for
platforms that require this support.

It is important to note that this logic is fundamental to the board
configuration process such as DDR configuration which is needed in
SPL, hence cannot be part of the standard u-boot driver model (which
is available later in the process). Hence, to aid efficiency, the
eeprom contents are copied over to SRAM scratchpad memory area at the
first invocation to retrieve data.

To prevent churn with cases such as DRA7, where eeprom format maybe
incompatible, we introduce a generic common format in eeprom which
is made available over accessor functions for usage.

Special handling for BBG1 EEPROM had to be introduced thanks to the
weird eeprom rev contents used.

The follow on patches introduce the use of this library for AM335x,
AM437x, and AM57xx.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Steve Kipisz <s-kipisz2@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>