Fix APB_CLK_FREQ value for C6 (IDFGH-11886)

[majkrzak]

This PR changes previously wrong value of APB_CLK_FREQ. It solves the issue with RMT LED driver where pulse with where incorrectly calculated using 40 MHz instead of 80 MHz clock base.

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[suda-morris]

Hi @majkrzak

The APB clock frequency is true to be 40MHz, but just on esp32c6, the APB clock can not work as a function clock for the RMT. Instead, the supported clock sources are listed here It has a PLL clock source whose frequency is 80MHz, but it's not APB anymore.

If you wants to write some code to work cross the esp chips, you can set the RMT clock source to RMT_CLK_SRC_DEFAULT. Like this

[majkrzak]

Ok thank you. This mean ESP-idf documentation is wrong. It claims RMT is clocked with APB clock with default frequency of 80MHz. And we had wrongly used the ABP_CLK_DIV macro to provide proper value. I believe there is none congaing the proper value for the RMT clock?