firmware: qcom_scm-64: Improve SMC convention detection

firmware: qcom_scm-64: Improve SMC convention detection

Improve the calling convention detection to use
__qcom_scm_is_call_available() and not blindly assume 32-bit mode if
the checks fails. BUG() if neither 32-bit or 64-bit mode works.

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/1578431066-19600-9-git-send-email-eberman@codeaurora.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>