[nrf fromtree] usb: device_next: msc: Implement double buffering

Double buffering make it possible to significantly increase the transfer
rates by avoiding idle states. With two SCSI buffers, one buffer can be
used by disk subsystem while the other is being used by UDC (ideally
with DMA).

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>
(cherry picked from commit 1243aba)

Author: tmon-nordic

subsys/usb/device_next/class/Kconfig.msc

@@ -30,6 +30,13 @@ config USBD_MSC_SCSI_BUFFER_SIZE
 	  Buffer size must be able to hold at least one sector. All LUNs within
 	  single instance share the SCSI buffer.
 
+config USBD_MSC_DOUBLE_BUFFERING
+	bool "SCSI double buffering"
+	default y
+	help
+	  Allocate two SCSI buffers instead of one to increase throughput by
+	  using one buffer by disk subsystem and one by USB at the same time.
+
 module = USBD_MSC
 module-str = usbd msc
 default-count = 1