Improved SD support

* Enable background operation support (in practice, interrupts were correctly
  specified in this case, but SDIODriver requires higher HAL device versions
  before trusting us).
* Set up the GPIO lines controlling the WiFi/Bluetooth module. Previously,
  these were floating, leading to intermittent responses on the SD bus
  depending on recent activity. Pad configuration is copied from the Linux
  device tree, and the pattern of high/low voltages were determined
  empirically.
11 jobs for !2 with SDIO in 8 seconds (queued for 26 seconds)
detached
Status Job ID Name Coverage
  Static Analysis
passed #55486
cross
copyright

00:00:00

passed #55477
cross
gitattributes

00:00:00

passed #55478
cross
gitignore

00:00:00

passed #55481
cross
head_log

00:00:00

passed #55484
cross
head_whitesp

00:00:00

passed #55479
cross
license

00:00:00

passed #55483
cross
makefile

00:00:00

passed #55482
cross
merge_log

00:00:00

passed #55485
cross
merge_whitesp

00:00:00

passed #55480
cross
versionnum

00:00:00

 
  Cleanup
passed #55487
cross
cleanup

00:00:00