Improve understandability of SMC macros by reversing the logic as they
are all functions of how many arguments can be shoved in registers and
how many SCM arguments are supported.

There aren't 4 register arguments because are 7 arguments that go into a
buffer - there are up to 7 arguments that are overflowed into a buffer
because only 4 registers are allocated for arguments.
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Tested-by: Brian Masney <masneyb@onstation.org> # arm32
Tested-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Elliot Berman <eberman@codeaurora.org>
Link: https://lore.kernel.org/r/1578431066-19600-5-git-send-email-eberman@codeaurora.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>