Make to flush the secondary cache when syncing PTEs when the Sheeva L2 cache
is used.
Appease gcc 4.8 -Wunused-but-set-variable warnings.
Check a status code and return proper errno in sdstrategy().

Suggested by gcc 4.8 -Wunused-but-set-variable warning to use the variable.
Use booted device unit if no unit number is specified on boot command.

Bump version to denote a visible change.
Put back "-Wa,-march=m68000 -Wa,-mcpu=m68000" for AFLAGS for X68000 models.

See my post in source-changes-d@ for details.
http://mail-index.netbsd.org/source-changes-d/2014/04/15/msg006723.html

Also use "-m68000" for CFLAGS for consistency.
(the previous -m68020-60 was harmless because vers.c has
 only const strings and there is no instruction)