spi: spi-geni-qcom: Don't wait to start 1st transfer if transmitting

If we're sending bytes over SPI, we know the FIFO is empty at the
start of the transfer.  There's no reason to wait for the interrupt
telling us to start--we can just start right away.  Then if we
transmit everything in one swell foop we don't even need to bother
listening for TX interrupts.

In a test of "flashrom -p ec -r /tmp/foo.bin" interrupts were reduced
from ~30560 to ~29730, about a 3% savings.

This patch looks bigger than it is because I moved a few functions
rather than adding a forward declaration.  The only actual change to
geni_spi_handle_tx() was to make it return a bool indicating if there
is more to tx.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Akash Asthana <akashast@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20200912111716.1.Ied5e843fad0d6b733a1fb8bcfb364dd2fa889eb3@changeid


Signed-off-by: Mark Brown <broonie@kernel.org>