esp.c: consolidate DMA and PDMA logic in MESSAGE OUT phase

esp.c: consolidate DMA and PDMA logic in MESSAGE OUT phase

This allows the removal of duplicate logic shared between the two implementations.
Note that we restrict esp_raise_drq() to PDMA to help reduce the log verbosity
for normal DMA.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: Helge Deller <deller@gmx.de>
Tested-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20240112125420.514425-81-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>