soc: mimxrt1064: Enable low power clocking for mimxrt1064

Enables low power clocks for mimxrt1064. This allows the soc to
transition into very low power states during idle, as most PLLs can be
disabled. Power states need to be enabled and selected at the board
level.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>