sysutils/cpu-microcode: merge the plugin code bases using variants

Should have done this from the start, but now this looks much cooler.  ;)

sysutils/cpu-microcode/src/etc/rc.loader.d/40-cpu-microcode.in

@@ -0,0 +1,2 @@
+cpu_microcode_load="YES"
+cpu_microcode_name="/boot/firmware/%%PLUGIN_VARIANT%%-ucode.bin"

sysutils/cpu-microcode/src/etc/rc.syshook.d/early/40-cpu-microcode

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+export microcode_update_enable="YES"
+
+/usr/local/etc/rc.d/microcode_update start