rom.sh: Name pico directory serprog_pico

Previously serprog_rp2040, but we now also support
the RP2530 boards.

Therefore, serprog_pico is a nice generic name. The
directory on release archives will now be serprog_pico
instead of serprog_rp2040; it will contain serprog images
for both RP2040 and RP2530 devices.

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

include/vendor.sh

@@ -375,7 +375,8 @@ detect_board()
 readcfg()
 {
 	if [ "$board" = "serprog_rp2040" ] || \
-	    [ "$board" = "serprog_stm32" ]; then
+	    [ "$board" = "serprog_stm32" ] || \
+	    [ "$board" = "serprog_pico" ]; then
 		return 1
 	fi; boarddir="$cbcfgsdir/$board"
 	eval `setcfg "$boarddir/target.cfg"`; chkvars vcfg tree