Fix only PWM 0 being enabled via Pinmux

[AlexJones0]

Currently, all the PWMs (minus the LCD backlight) are being routed through pinmux, but the value being passed for the PWM output enable is the constant '{'b1}. Because the inner value is 'b1, this is extended to fill the 7 bit PWM output range as 0000001, instead of using '1 which would extend to 1111111. Hence, to fix this, we would want to use the value '{'1} instead.

Thanks to @elliotb-lowrisc who came up with a slightly more robust and comprehensible alternative, where we more explicitly cast/extend these values to match the output size and module count. These changes should probably be propagated to the other port connections (e.g. SPI), but are isolated to just PWM for this PR to keep this PR focused on fixing the bug. This ensures that all outputs of all PWM devices are now enabled through pinmux.

I've tested this fix makes the correct values appear on the waveforms in simulation, and I've built a bitstream and tested muxing pwm_out_1 to PMOD0_2 and using a digtal multimeter to read a range of values, which wasn't working previously. The code snippet used for testing is as below:

auto pinmux = SonataPinmux();
auto pwm = MMIO_CAPABILITY(SonataPwm, pwm);

pinmux.output_pin_select(SonataPinmux::OutputPin::pmod0_2, 3); // Pinmux PMOD0_2 to PWM_OUT_1
pwm->output_set(1, 255, 255);

Edit: I've also now manually tested (again on FPGA using a multimeter) every single possible mux of PWM/pin - all seem to be working as expected.

[marnovandermaas]

Yup, this looks correct to me. I'm a bit annoyed this wasn't flagged as a lint error. I've double checked the syntax using this toy example: https://codeberg.org/marno/toy-verilator/src/branch/main/array_width/array_width.v