ARM: OMAP2420: hwmod data/PM: use hwmod to block WFI when I2C active

Use the HWMOD_BLOCK_WFI flag in the hwmod data to prevent the MPU from
entering WFI when the I2C devices are active.  No idea why this is needed;
this could certainly bear further investigation if anyone is interested.
The objective here is to remove some custom code from the OMAP24xx PM
code.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>