arm: am33xx: Add support for mulitiple PLL input frequencies

am335x supports various sysclk frequencies which can be determined
using sysboot pins. PLLs should be configures based on this
sysclk frequency. Add PLL configurations for all supported
frequencies.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>