Enable IO20 on ESP32

Some newer ESP32 variants (like ESP32-PICO-V3 and ESP32-PICO-MINI-02)
do implement this pin and it can be used as a normal GPIO.

Fixes #6016
Fixes #6837

Closes https://github.com/espressif/esp-idf/pull/6918

(cherry picked from commit 6deaefde69c3f068d39b76d628b05b21fd142b79)

components/soc/esp32/gpio_periph.c

@@ -35,7 +35,7 @@ const uint32_t GPIO_PIN_MUX_REG[SOC_GPIO_PIN_COUNT] = {
     IO_MUX_GPIO17_REG,
     IO_MUX_GPIO18_REG,
     IO_MUX_GPIO19_REG,
-    0,
+    IO_MUX_GPIO20_REG, // This corresponding pin is only available on ESP32-PICO-V3 chip package
     IO_MUX_GPIO21_REG,
     IO_MUX_GPIO22_REG,
     IO_MUX_GPIO23_REG,

components/soc/esp32/include/soc/soc_caps.h

@@ -114,8 +114,8 @@
 // set pullup/down/capability via RTC register. On ESP32-S2, Digital IOs have their own registers to
 // control pullup/down/capability, independent with RTC registers.
 
-// 0~39 except from 20, 24, 28~31 are valid
-#define SOC_GPIO_VALID_GPIO_MASK        (0xFFFFFFFFFFULL & ~(0ULL | BIT20 | BIT24 | BIT28 | BIT29 | BIT30 | BIT31))
+// 0~39 except from 24, 28~31 are valid
+#define SOC_GPIO_VALID_GPIO_MASK        (0xFFFFFFFFFFULL & ~(0ULL | BIT24 | BIT28 | BIT29 | BIT30 | BIT31))
 // GPIO >= 34 are input only
 #define SOC_GPIO_VALID_OUTPUT_GPIO_MASK (SOC_GPIO_VALID_GPIO_MASK & ~(0ULL | BIT34 | BIT35 | BIT36 | BIT37 | BIT38 | BIT39))