mmc: core: Parse and use the new max-sd-hs-hz DT property

Introduce a new device tree flag to cap the maximum High-Speed (HS)
mode frequency for SD cards, accommodating board-specific
electrical limitations which cannot support the default 50Mhz HS
frequency and others.

Signed-off-by: Sarthak Garg <quic_sartgarg@quicinc.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>