config/git: use "depend" for serprog dependencies

this brings the handling of serprog projects in sync
with canoeboot, which relies on the "depend" variable
to get the needed submodules, because cbmk does not
download submodules for these projects

lbmk does download submodules. i want it in sync with
cbmk for this, to make merging easier between both
projects, because i'm going to make a change on both
projects, whereby config/submodules/ is used exclusively

Signed-off-by: Leah Rowe <leah@libreboot.org>

config/git/stm32-vserprog

@@ -3,4 +3,12 @@
 	loc: stm32-vserprog
 	url: https://codeberg.org/libreboot/stm32-vserprog
 	bkup_url: https://git.disroot.org/libreboot/stm32-vserprog
+	depend: libopencm3
+}
+
+{libopencm3}{
+	rev: 458250dc6147dc807eec9e4d5a6caf38a699ecb1
+	loc: stm32-vserprog/libopencm3
+	url: https://codeberg.org/libreboot/libopencm3
+	bkup_url: https://github.com/libopencm3/libopencm3
 }