clk: lan966x: Extend lan966x clock driver for clock gating support

Extend the clock driver to add support also for clock gating. The
following peripherals can be gated: UHPHS, UDPHS, MCRAMC, HMATRIX.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20211103085102.1656081-5-horatiu.vultur@microchip.com