[RFC PATCH 0/3] blk-mq: Allow to complete requests directly

This is a follow up to
  https://lkml.kernel.org/r/20201102181238.GA17806@infradead.org

where I *think* we agreed to audit driver which complete their blk
request from process context and then let them complete the request
directly instead going through ksoftirqd.

This series converts a part from the MMC layer which completes the
requests from kworker/ preemptible context. It was verified with
sdhci-pci device under normal usage. It also converts the usb-storage
driver which is slightly complicated since it goes through the SCSI
layer.

Sebastian