sdcard: support thingplus-rp2040

The instances of SPI interfaces SPI0, SPI1, ... are
pointers to SPI types on rp2040 machines, rather plain
values like other machines.

This needs restructuring the sdcard API to take a pointer
to the SPI interface rather the SPI type itself.

Removed waitserial() since it needs modem control lines
not available on most boards

sdcard/sdcard.go

@@ -28,7 +28,7 @@ var (
 )
 
 type Device struct {
-	bus        machine.SPI
+	bus        *machine.SPI
 	sck        machine.Pin
 	sdo        machine.Pin
 	sdi        machine.Pin
@@ -41,7 +41,7 @@ type Device struct {
 	CSD        *CSD
 }
 
-func New(b machine.SPI, sck, sdo, sdi, cs machine.Pin) Device {
+func New(b *machine.SPI, sck, sdo, sdi, cs machine.Pin) Device {
 	return Device{
 		bus:        b,
 		cs:         cs,