ARM: OMAP4: hwmod data: make *phy_48m* as the main_clk of ocp2scp

Made *ocp2scp_usb_phy_phy_48m* as the main_clk for ocp2scp.
Since this ocp2scp module does not have any fck but does have a
single opt_clock, it is added as the main_clk for ocp2scp. Also
removed phy_48m as the optional clock since it is now made as the
main clock. By this the driver need not enable/disable phy_48m clk
separately and runtime_get/runtime_put will take care of that.

Cc: Benoît Cousson <b-cousson@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Benoît Cousson <b-cousson@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>