clk: at91: check pmc node status before registering syscore ops

Currently, at91 pmc driver always register the syscore_ops whatever
the status of the pmc node that has been found. When set as secure
and disabled, the pmc should not be accessed or this will generate
abort exceptions.
To avoid this, add a check on node availability before registering
the syscore operations.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Link: https://lore.kernel.org/r/20210913082633.110168-1-clement.leger@bootlin.com


Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Fixes: b3b02eac ("clk: at91: Add sama5d2 suspend/resume")
Signed-off-by: Stephen Boyd <sboyd@kernel.org>