arm: omap3: Enable clocks for peripherals only if they are used

This patch change the per_clocks_enable() function used in OMAP3
code to enable peripherals clocks. Only required clock should be
activated. So if the board use the uart(x) as a console we need
to activate it. The Board's config should include define to enable
every subsystem that the board use. For a complete list
of affected peripherals, registers CM_FCLKEN_PER and CM_ICLKEN_PER
should be checked.
Right now the bootloader can enable and disable clocks for:
uart(x) using CONFIG_SYS_NS16550
gpio bank (x) using CONFIG_OMAP3_GPIO_X with X = { 2, 3, 4, 5, 6 }
i2c bus using CONFIG_DRIVER_OMAP34XX_I2C.

Not required gptimer(x) and mcbsp(x) for booting are disabled by default and
are not supported by any define.
Their activation need to included in the per_clocks_enable if the
peripheral is included. Not booting board should enable the peripheral
clock connected to their driver

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Tom Rini <trini@ti.com>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>