dt-bindings: firmware: scm: Add compatible for msm8226

Add devicetree compatible for SCM present in msm8226 platform.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210911232707.259615-4-luca@z3ntu.xyz