dt-bindings: mmc: sdhci-msm: Add compatible string for msm8226

Add msm8226 SoC specific compatible strings for qcom-sdhci controller.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Link: https://lore.kernel.org/r/20210911232707.259615-3-luca@z3ntu.xyz
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>