ti: i2c: Convert CONFIG_SYS_OMAP24_I2C to CONFIG_SYS_I2C namespace

ti: i2c: Convert CONFIG_SYS_OMAP24_I2C to CONFIG_SYS_I2C namespace

The omap24xx I2C driver uses its own CONFIG namespace for common I2C
variables.  Rather than convert more of them to Kconfig, rename these to
the common I2C ones and remove the entirely unused functionality.  As
part of this, we make the am335x_shc platforms consistent with their
intended speed values.

Signed-off-by: Tom Rini <trini@konsulko.com>