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The branch_if_master macro jumps to a label if the CPU is the "master" core, which we define as having all affinity levels set to 0. To check for this condition, we need to mask off some bits from the MPIDR register, then compare the remaining register value against zero. The implementation of this was slighly broken (it preserved the upper RES0 bits), overly complicated and hard to understand, especially since it lacked comments. The same was true for the very similar branch_if_slave macro. Use a much shorter assembly sequence for those checks, use the same masking for both macros (just negate the final branch), and put some comments on them, to make it clear what the code does. This allows to drop the second temporary register for branch_if_master, so we adjust all call sites as well. Also use the opportunity to remove a misleading comment: the macro works fine on SoCs with multiple clusters. Judging by the commit message, the original problem ...
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