ptp: ocp: Simplify Kconfig.

Remove the 'imply' statements, these apparently are not doing
what I expected.  Platform modules which are used by the driver
still need to be enabled in the overall config for them to be
used, but there isn't a hard dependency on them.

Use 'depend' for selectable modules which provide functions
used directly by the driver.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: David S. Miller <davem@davemloft.net>