support uart that defaults to PLL_F80M

[eteq]

On an esp32c6 with idf 5.1.1 (devkitC, although I doubt that matters), I could not for the life of me get the uart example to work. Eventually I figured out that, at least in my particular setup, the default clock for the UART is the PLL_F80M clock... which must not have existed in earlier IDFs (or maybe it's particular to the esp32c6? Not sure, but it doesn't really matter).

This PR simply adds support in for the UART_SCLK_PLL_F80M clock source, since without this I couldn't get past a panic from creating the default uart config.

[eteq]

Well that's odd - this works locally for me, but the CI is failing. I suppose it must be the #[cfg(all(esp_idf_version_major = "4", esp_idf_soc_uart_support_pll_f80m_clk))] element, but why would that be failing on the 5.1 builds and the 4.x builds?

[ivmarkov]

@eteq Run cargo fmt on the PR.

[t-moe]

I run into the same problem today.

Simply invoking uart::config::Config::new() will panic on esp32c6 with esp_idf 5.1. This PR seems to fix that.

[ivmarkov]

Thanks!