Add grapefruit/app-mini.toml (#2264)

While debugging #2236, I wanted a tiny image that produced compact
system dumps – they're faster to load in a debug build of Humility, and
we'll eventually want to commit one to the Humility test suite.

This image produces a 421KiB dump, versus 7 MiB for a full Cosmo image.
It's just enough to blink an LED so that you know it's been flashed and
is running.

Author: mkeeter

app/grapefruit/app-mini.toml

@@ -0,0 +1,51 @@
+# Tiny Grapefruit image, mostly for testing Humility
+board = "grapefruit"
+name = "grapefruit-mini"
+target = "thumbv7em-none-eabihf"
+chip = "../../chips/stm32h7"
+memory = "memory-large.toml"
+stacksize = 512
+
+[kernel]
+name = "grapefruit"
+requires = {flash = 32768, ram = 2048}
+features = ["measurement-handoff"]
+extern-regions = ["dtcm"]
+
+[tasks.jefe]
+name = "task-jefe"
+priority = 0
+start = true
+notifications = ["fault", "timer"]
+extern-regions = ["sram1", "sram2", "sram3", "sram4"]
+
+[tasks.jefe.config.allowed-callers]
+set_reset_reason = ["sys"]
+
+[tasks.sys]
+name = "drv-stm32xx-sys"
+features = ["h753"]
+priority = 1
+uses = ["rcc", "gpios", "system_flash", "syscfg"]
+start = true
+task-slots = ["jefe"]
+
+[tasks.user_leds]
+name = "drv-user-leds"
+features = ["stm32h7"]
+priority = 5
+start = true
+task-slots = ["sys"]
+notifications = ["timer"]
+
+[tasks.pong]
+name = "task-pong"
+priority = 8
+start = true
+task-slots = ["user_leds"]
+notifications = ["timer"]
+
+[tasks.idle]
+name = "task-idle"
+priority = 9
+start = true

drv/user-leds/src/main.rs

@@ -97,6 +97,7 @@ cfg_if::cfg_if! {
         target_board = "psc-b",
         target_board = "psc-c",
         target_board = "oxcon2023g0",
+        target_board = "grapefruit",
     ))] {
         #[derive(enum_map::Enum, Copy, Clone, FromPrimitive)]
         enum Led {