Make all the modules build on arm (modulo ipfilter, which I'm looking

into):

o Don't build vpo and syscons on mips or arm either
o Add a section for mips and arm breakages, and document why.
  This is easier than opting in on all the other architectures:
  # no BUS_SPACE_UNSPECIFIED: bce, bwi, bwn, mfi, mpt, siba_bwn
  # No barrier instruction support (specific to this driver): sym
  # no uart_cpu_$MACHINE_ARCH: uart

(mips has, by inspection, the same issues as arm, so ditto for it)

MFC after:	7 days

sys/modules/Makefile

@@ -34,15 +34,15 @@ SUBDIR=	${_3dfx} \
 	ata \
 	ath \
 	${_auxio} \
-	bce \
+	${_bce} \
 	bfe \
 	bge \
 	${_bios} \
 	${_bktr} \
 	${_bm} \
 	bridgestp \
-	bwi \
-	bwn \
+	${_bwi} \
+	${_bwn} \
 	cam \
 	${_canbepm} \
 	${_canbus} \
@@ -66,7 +66,7 @@ SUBDIR=	${_3dfx} \
 	${_cryptodev} \
 	${_cs} \
 	${_ctau} \
-	cxgb \
+	${_cxgb} \
 	${_cyclic} \
 	dc \
 	dcons \
@@ -175,13 +175,13 @@ SUBDIR=	${_3dfx} \
 	mcd \
 	md \
 	mem \
-	mfi \
+	${_mfi} \
 	mii \
 	mlx \
 	${_mly} \
 	mmc \
 	mmcsd \
-	mpt \
+	${_mpt} \
 	mqueue \
 	msdosfs \
 	msdosfs_iconv \
@@ -251,7 +251,7 @@ SUBDIR=	${_3dfx} \
 	sdhci \
 	sem \
 	sf \
-	siba_bwn \
+	${_siba_bwn} \
 	siis \
 	sis \
 	sk \
@@ -268,7 +268,7 @@ SUBDIR=	${_3dfx} \
 	stge \
 	${_streams} \
 	${_svr4} \
-	sym \
+	${_sym} \
 	${_syscons} \
 	sysvipc \
 	ti \
@@ -279,7 +279,7 @@ SUBDIR=	${_3dfx} \
 	twe \
 	tx \
 	txp \
-	uart \
+	${_uart} \
 	ubsec \
 	udf \
 	udf_iconv \
@@ -312,11 +312,26 @@ SUBDIR=	${_3dfx} \
 	${_zfs} \
 	zlib \
 
-.if ${MACHINE_ARCH} != "powerpc"
+.if ${MACHINE_ARCH} != "powerpc" && ${MACHINE_ARCH} != "arm" && \
+	${MACHINE_ARCH} != "mips"
 _syscons=	syscons
 _vpo=		vpo
 .endif
 
+.if ${MACHINE_ARCH} != "arm" && ${MACHINE_ARCH} != "mips"
+# no BUS_SPACE_UNSPECIFIED
+_bce=		bce
+_bwi=		bwi
+_bwn=		bwn
+_mfi=		mfi
+_mpt=		mpt
+_siba_bwn=	siba_bwn
+# No barrier instruction support (specific to this driver)
+_sym=		sym
+# no uart_cpu_$MACHINE_ARCH
+_uart=		uart
+.endif
+
 .if ${MK_CRYPT} != "no" || defined(ALL_MODULES)
 .if exists(${.CURDIR}/../opencrypto)
 _crypto=	crypto