mgb: Build module for all archs

It is not x86-specific.

This reverts commit e0a5aa37c1.
This reverts commit 2d935a1e93.

Reviewed by:	kbowling
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D60615

share/man/man4/Makefile

@@ -797,7 +797,7 @@ MLINKS+=me.4 if_me.4
 MLINKS+=mem.4 kmem.4
 MLINKS+=mfi.4 mfi_linux.4 \
 	mfi.4 mfip.4
-MLINKS+=${_mgb.4} ${_if_mgb.4}
+MLINKS+=mgb.4 if_mgb.4
 MLINKS+=mlx5en.4 mce.4 \
 	mlx5en.4 if_mce.4
 MLINKS+=mos.4 if_mos.4
@@ -914,7 +914,6 @@ _i8254.4=	i8254.4
 _ichwd.4=	ichwd.4
 _if_bxe.4=	if_bxe.4
 _if_hn.4=	if_hn.4
-_if_mgb.4=	if_mgb.4
 _if_nfe.4=	if_nfe.4
 _if_urtw.4=	if_urtw.4
 _if_wpi.4=	if_wpi.4

share/man/man4/mgb.4

@@ -22,7 +22,7 @@
 .\" SUCH DAMAGE.
 .\"
 .Dd September 28, 2021
-.Dt MGB 4 amd64
+.Dt MGB 4
 .Os
 .Sh NAME
 .Nm mgb

sys/modules/Makefile

@@ -257,7 +257,7 @@ SUBDIR=	\
 	${_mana} \
 	md \
 	mdio \
-	${_mgb} \
+	mgb \
 	mem \
 	mfi \
 	mii \
@@ -785,7 +785,6 @@ _ixv=		ixv
 _lio=		lio
 .endif
 _mana=		mana
-_mgb=		mgb
 _nctgpio=	nctgpio
 _ncthwm=	ncthwm
 _ntb=		ntb