cpu/esp32: revise CAN support

CAN interface is now supported in RIOT. Change feature table
accordingly.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

cpu/esp32/doc.txt

@@ -153,7 +153,7 @@ UARTs       | 3 | yes
 WiFi        | IEEE 802.11 b/g/n built in | yes
 Bluetooth   | v4.2 BR/EDR and BLE | no
 Ethernet    | MAC interface with dedicated DMA and IEEE 1588 support | yes
-CAN         | version 2.0 | no
+CAN         | version 2.0 | yes
 IR          | up to 8 channels TX/RX | no
 Motor PWM   | 2 devices x 6 channels | yes
 LED PWM     | 16 channels | no
@@ -176,6 +176,7 @@ The RIOT-OS for ESP32 SoCs supports the following features at the moment:
 - I2C interfaces
 - SPI interfaces
 - UART interfaces
+- CAN interface
 - CPU ID access
 - RTC module
 - ADC and DAC channels