firmware: exynos-acpm: Count number of commands in acpm_xfer

firmware: exynos-acpm: Count number of commands in acpm_xfer

Struct acpm_xfer holds two buffers with u32 commands - rxd and txd - and
counts their size by rxlen and txlen.  "len" suffix is here ambiguous,
so could mean length of the buffer or length of commands, and these are
not the same since each command is u32.  Rename these to rxcnt and
txcnt, and change their usage to count the number of commands in each
buffer.

This will have a benefit of allowing to use __counted_by_ptr later.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Link: https://patch.msgid.link/20260219-firmare-acpm-counted-v2-2-e1f7389237d3@oss.qualcomm.com
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>