rp/pio: configure state machines with Config struct

the many individual sets aren't very efficient, and almost no checks
were done to ensure that the configuration written to the hardware was
actually valid. this adresses both of these.

examples/rp/Cargo.toml

@@ -22,6 +22,8 @@ lorawan = { version = "0.7.3", default-features = false, features = ["default-cr
 
 defmt = "0.3"
 defmt-rtt = "0.4"
+fixed = "1.23.1"
+fixed-macro = "1.2"
 
 #cortex-m = { version = "0.7.6", features = ["critical-section-single-core"] }
 cortex-m = { version = "0.7.6", features = ["inline-asm"] }