arm: omap4: pandaboard: turn on PHY reference clock at init

The SMSC 3320 USB PHY on the OMAP4 Pandaboard needs a 19.2 MHz
reference clock. This clock is provided from the OMAP4's fref_clk3
pad.

Recent changes to clock44xx_data.c made the clock framework aware
of the existence of these fref_clk[i] lines. If the option
CONFIG_OMAP_RESET_CLOCKS is enabled in the kernel, then the
clock framework will turn these clocks off during bootup.

Explicitly request and keep this clock enabled at init for the
Pandaboard, so that the PHY receives this clock at all times.

Reported-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Reviewed-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>