fix typos, deal with hardware insanity
use SX for basic hardware acceleration
not quite complete yet but good enough to be useful
missing things include:
- backwards blits
- ROP support
- the cursor is still drawn by software
Modify earm rule to match any machine_arch starting with earm.
gcc will supply -Wa,-eabi=gnu so don't include.  Use -mabi=apcs-base, not atpcs
Test taking a snapshot from a stressed file system.
Checks snapshot meta data only with fsck.

OK: Antti Kantee <pooka@netbsd.org>
Take fss_device_lock first when closing a fss device.

Fixes PR kern/47514 (Multiple dump -X triggers kernel panic in fss_ioctl)
Lookup the block device mounted on from the specfs_hash table.
This doesn't belong here but makes it possible to pullup.

Fixes PR kern/47020 (fss(4) panic)
fix broken logic:
- poll can return EINTR, it is not restartable like read/write
- check poll return
- it does not make sense to check readyfd() is nready < 0
- check read return
- always call Job_CatchChildren, it is harmless
- short circuit scanning of the poll array if we got all the ready descriptors
merry belated x-mas.
reorg and add missing file.
add SX_ROP instruction