Update guide for using updated pinmux driver interface

Sonata's Pinmux driver has been updated to give it more granaular
capabilites, such that capabilities to individual pin sinks and block
sinks can be created and distributed, for better compartmentalisation
and isolation of software that uses pinmux.

This commit updates `sonata-software` to use the updated driver.
Currently, the only thing using Pinmux in the software repo is the IO
guide, and so this is updated to reflect the new software interface for
this driver.

Author: AlexJones0

doc/guide/sonata-io.md

@@ -35,18 +35,25 @@ For example say you wished to connect the PMOD0 SPI to SPI block 1; there are 4
 - PMOD 0 CS (pin 1), COPI (pin 2) and SCK (pin 4) output selectors
 - SPI Block 1 CIPO input selector
 
-The code below shows how to use the pinmux driver to do this:
+The code below shows how you could use the pinmux driver to do this:
 
 ```c++
 #include <platform-pinmux.hh>
 
 ...
 
-auto pinmux = SonataPinmux();
-pinmux.output_pin_select(SonataPinmux::OutputPin::pmod0_1, 2);
-pinmux.block_input_select(SonataPinmux::BlockInput::spi_1_cipo, 3);
-pinmux.output_pin_select(SonataPinmux::OutputPin::pmod0_2, 2);
-pinmux.output_pin_select(SonataPinmux::OutputPin::pmod0_4, 2);
+auto pinmuxPinSinks = MMIO_CAPABILITY(SonataPinmux::PinSinks, pinmux_pins_sinks);
+auto pinmuxBlockSinks = MMIO_CAPABILITY(SonataPinmux::BlockSinks, pinmux_block_sinks);
+
+auto pmod0_1 = pinmuxPinSinks->get(SonataPinmux::PinSink::pmod0_1);
+auto spi_1_cipo = pinmuxBlockSinks->get(SonataPinmux::BlockSink::spi_1_cipo);
+auto pmod0_2 = pinmuxPinSinks->get(SonataPinmux::PinSink::pmod0_2);
+auto pmod0_4 = pinmuxPinSinks->get(SonataPinmux::PinSink::pmod0_4);
+
+pmod0_1.select(2);
+spi_1_cipo.select(3);
+pmod0_2.select(2);
+pmod0_4.select(2);
 ```
 
 Following this you can then use the `spi1` SPI instance to communicate with whatever SPI device is plugged into PMOD0.