Use formula-based description instead of incomplete GPIO pin lists

Addresses review feedback: the hard-coded pin lists only covered RP2040
GPIOs and were incomplete for RP2350 (GPIO up to 47). Now describes the
(gpio / 2) % 2 rule instead.

esphome/components/i2c/__init__.py

@@ -178,9 +178,10 @@ def _final_validate(config):
             if len(set(controllers)) != len(controllers):
                 raise cv.Invalid(
                     "Multiple I2C buses are configured to use the same I2C controller. "
-                    "Each bus must use pins on a different controller "
-                    "(I2C0: SDA on GPIO 0,4,8,12,16,20,24,28; "
-                    "I2C1: SDA on GPIO 2,6,10,14,18,22,26)."
+                    "Each bus must use pins on a different controller. "
+                    "The I2C controller is determined by (gpio / 2) % 2: "
+                    "even pin pairs (0-1, 4-5, 8-9, ...) use I2C0, "
+                    "odd pin pairs (2-3, 6-7, 10-11, ...) use I2C1."
                 )
     if CORE.is_esp32 and get_esp32_variant() in ESP32_I2C_CAPABILITIES:
         variant = get_esp32_variant()

esphome/components/i2c/i2c_bus_arduino.cpp

@@ -21,9 +21,9 @@ void ArduinoI2CBus::setup() {
   wire_ = new TwoWire();  // NOLINT(cppcoreguidelines-owning-memory)
 #elif defined(USE_RP2040)
   // Select Wire instance based on pin assignment, not definition order.
-  // RP2040 I2C controller is determined by GPIO: (pin / 2) % 2
-  // See RP2040 datasheet Table 2 (section 1.4.3): https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.pdf
-  // See RP2350 datasheet Table 7 (section 9.4): https://datasheets.raspberrypi.com/rp2350/rp2350-datasheet.pdf
+  // I2C controller = (gpio / 2) % 2: even pairs (0-1,4-5,...) → I2C0, odd pairs (2-3,6-7,...) → I2C1
+  // RP2040 datasheet Table 2 (section 1.4.3): https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.pdf
+  // RP2350 datasheet Table 7 (section 9.4): https://datasheets.raspberrypi.com/rp2350/rp2350-datasheet.pdf
   if ((this->sda_pin_ / 2) % 2 == 0) {
     wire_ = &Wire;
   } else {