spmi: msm: use real number of channels for v5 & v7

spmi: msm: use real number of channels for v5 & v7

The SPMI_MAX_CHANNELS_Vx are only the maximum channels supported
by the controller, but the real number of channels mapped on this
system can be read from a register, so take this info.

This allows no to overlap on the second controller present on
the V7 SPMI arbiter, otherwise we would also parse the mapping
of the second SPMI bus and we would bet the wrong IDs.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Tested-by: caleb.connolly@linaro.org # sdm845
Link: https://lore.kernel.org/r/20250328-topic-sm8x50-spmi-fix-v1-1-a7548d3aef0d@linaro.org
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>