omap4_common: config: remove I2C for SPL mode

Commit 6789e84e (i2c, omap24xx:
convert driver to new mutlibus/mutliadapter framework) intended to
make I2C driver compatible with latest changes. It unfortunately has
had a impact on size on SPL as well. For example on SDP4430,
32032 bytes before/MLO
35416 bytes after/MLO

With this mentioned commit, MLO stops booting on SDP4430 as only 32K
is accessible for non-secure (bootloader) s/w on GP devices and the size
increase to 56K fails boot.

On the latest u-boot commit e7be1822,
MLO is now at size 35592 bytes, However, I2C is not necessary for SPL
to function as we use SR_I2C for controlling the PMIC.
Disabling I2C reduces MLO to 32224 bytes which allows
OMAP4 GP platform to boot up.

Since this is common for all OMAP4 platforms, remove the need for I2C
for SPL builds in the common config.

Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Sricharan R <r.sricharan@ti.com>