Add EFI to kernel options.

Some parts of MI modules will soon depend on whether EFI is available
or not. Add EFI to the list of kernel options so we can use it in
the modules build.

sys/conf/kern.opts.mk

@@ -30,6 +30,7 @@ __DEFAULT_YES_OPTIONS = \
     CDDL \
     CRYPT \
     CUSE \
+    EFI \
     FORMAT_EXTENSIONS \
     INET \
     INET6 \
@@ -91,6 +92,11 @@ BROKEN_OPTIONS+= OFED
 BROKEN_OPTIONS+= KERNEL_RETPOLINE
 .endif
 
+# EFI doesn't exist on mips, powerpc, sparc or riscv.
+.if ${MACHINE:Mmips} || ${MACHINE:Mpowerpc} || ${MACHINE:Msparc64} || ${MACHINE:Mriscv}
+BROKEN_OPTIONS+=EFI
+.endif
+
 # expanded inline from bsd.mkopt.mk to avoid share/mk dependency
 
 # Those that default to yes