net: microchip: add registers needed for PSFP

Add registers needed for PSFP. This patch also renames a single
register, shortening its name (SYS_CLK_PER_100PS). Uses have been update
accordingly.

Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>