sdhci: fdt: Always enable clock for ZynqMP and RK3399

Those two (in fact all of the supported one in this driver except RK3568) always
needs the clocks to be enabled.

Reviewed-by: bz
Differential Revision: https://reviews.freebsd.org/D41808
Sponsored by: Beckhoff Automation GmbH & Co. KG

(cherry picked from commit 9377d7049c846d1e35c8fc8809c23e6413909fca)