USB: musb: blackfin: push clkin value to platform resources

In order to not touch the driver file for different xtal usage,
push the clkin value to board file and calculate the register
value instead of hardcoding it.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>