I2C device tree descriptions in TOML (#238)

This work adds a description of I2C in TOML as part of an application
definition, allowing this description to be pulled out of hand-written
code, and into code that is automatically generated as part of the
build process. This allows for Humility to know the I2C device tree
based on the archive -- which in turn allows for much more robust
tooling for I2C and I2C-based protcols like PMBus. In addition to
adding support for I2C in TOML and definitions for every platform that
supports I2C, this work also:

- Adds a preliminary Sidecar image
- Adds QSPI support for the Nucleo board
- Eliminates the notion of `Port::Default`
- Adds a HIF sleep function and I2C bulk write function
- Adds a HIF QSPI function to verify an image
- Corrects the HIF QSPI error conditions

Cargo.toml

@@ -18,6 +18,7 @@ members = [
     "kern",
     "ringbuf",
     "userlib",
+    "sidecar",
     "stage0",
     "hypocalls",
     "lpc55_romapi",

build-i2c/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "build-i2c"
+version = "0.1.0"
+authors = ["Bryan Cantrill <bryan@oxide.computer>"]
+edition = "2018"
+
+[dependencies]
+build-util = {path = "../build-util"}
+serde = { version = "1.0.114", features = ["derive"] }
+indexmap = { version = "1.4.0", features = ["serde-1"] }
+anyhow = "1.0.31"
+cfg-if = "0.1.10"
+multimap = "0.8.3"
+convert_case = "0.4"
+