soc/mediatek: Add function to measure clock frequency of MT8192

Implement mt_fmeter_get_freq_khz() in MT8192 to measure frequency of
some pre-defined clocks by frequency meter.

Signed-off-by: Weiyi Lu <weiyi.lu@mediatek.com>
Change-Id: I75df0b040ed7ea73d25724a3c80040f4e731118f
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45402
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/mediatek/common/include/soc/pll_common.h

@@ -60,4 +60,10 @@ int pll_set_rate(const struct pll *pll, u32 rate);
 void mt_pll_init(void);
 void mt_pll_raise_little_cpu_freq(u32 freq);
 
+enum fmeter_type {
+	FMETER_ABIST = 0,
+	FMETER_CKGEN,
+};
+u32 mt_fmeter_get_freq_khz(enum fmeter_type type, u32 id);
+
 #endif