Minor clock tree tweaks

[bugadani]

• This PR adds the PLL_F160M clock source to ESP32, which is a clock source of the MCPWM and I2S peripherals.
• This PR removes the unnecessary i2c_clock field from the cached global clock speed struct.

I wanted to remove more of the fields, but at least RNG needs a low-overhead way to read CPU and APB frequencies for throttling purposes, so the struct itself needs to stick around until a general strategy can replace it.

cc #4502

[Copilot]

Pull request overview

This PR enhances the ESP32 clock tree implementation by adding the PLL_F160M_CLK clock source and removing the redundant i2c_clock field from the cached clock configuration. The PLL_F160M_CLK is a 160 MHz clock derived from the PLL and serves as the clock source for MCPWM and I2S peripherals.

• Adds PLL_F160M_CLK definition to ESP32 clock tree metadata
• Updates pwm_clock to use the new PLL_F160M_CLK source instead of hardcoded 160 MHz
• Removes i2c_clock field and updates I2C drivers to query ClockTree directly
• Refactors MCPWM clock source retrieval into a helper method

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
esp-metadata/devices/esp32.toml	Adds PLL_F160M_CLK clock node definition derived from PLL_CLK
esp-metadata-generated/src/_generated_esp32.rs	Generates request/release/frequency functions and reference counting for PLL_F160M_CLK
esp-metadata-generated/src/_build_script_utils.rs	Adds build configuration flags for the new clock node
esp-hal/src/soc/esp32/clocks.rs	Implements enable_pll_f160m_clk_impl as no-op since clock is always available when PLL is enabled
esp-hal/src/mcpwm/mod.rs	Refactors clock source retrieval into source_clock() helper method
esp-hal/src/i2c/master/mod.rs	Removes Clocks import and updates set_frequency implementations to query ClockTree directly
esp-hal/src/clock/mod.rs	Removes i2c_clock field and updates pwm_clock to use pll_f160m_clk_frequency()

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