rp: hook up softfloat rom intrinsics

rp-hal has done this very well already, so we'll just copy their entire
impl again. only div.rs needed some massaging because our sio access
works a little differently, everything else worked as is.

embassy-rp/src/lib.rs

@@ -12,6 +12,7 @@ mod intrinsics;
 
 pub mod adc;
 pub mod dma;
+mod float;
 pub mod gpio;
 pub mod i2c;
 pub mod interrupt;