doc: sipeed: adopt zephyr:board-supported-hw directive

Replace manually authored hardware features table with the new Zephyr
board supported hardware directive which automatically generates an
up-to-date table based on the boards' Devicetree.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

boards/sipeed/longan_nano/doc/index.rst

@@ -35,41 +35,7 @@ Hardware
 Supported Features
 ==================
 
-The board configuration supports the following hardware features:
-
-.. list-table::
-   :header-rows: 1
-
-   * - Peripheral
-     - Kconfig option
-     - Devicetree compatible
-   * - GPIO
-     - :kconfig:option:`CONFIG_GPIO`
-     - :dtcompatible:`gd,gd32-gpio`
-   * - Machine timer
-     - :kconfig:option:`CONFIG_RISCV_MACHINE_TIMER`
-     - :dtcompatible:`riscv,machine-timer`
-   * - Nuclei ECLIC Interrupt Controller
-     - :kconfig:option:`CONFIG_NUCLEI_ECLIC`
-     - :dtcompatible:`nuclei,eclic`
-   * - PWM
-     - :kconfig:option:`CONFIG_PWM`
-     - :dtcompatible:`gd,gd32-pwm`
-   * - USART
-     - :kconfig:option:`CONFIG_SERIAL`
-     - :dtcompatible:`gd,gd32-usart`
-   * - I2C
-     - :kconfig:option:`CONFIG_I2C`
-     - :dtcompatible:`gd,gd32-i2c`
-   * - DAC
-     - :kconfig:option:`CONFIG_DAC`
-     - :dtcompatible:`gd,gd32-dac`
-   * - ADC
-     - :kconfig:option:`CONFIG_ADC`
-     - :dtcompatible:`gd,gd32-adc`
-   * - SPI
-     - :kconfig:option:`CONFIG_SPI`
-     - :dtcompatible:`gd,gd32-spi`
+.. zephyr:board-supported-hw::
 
 The microSD card reader in Longan Nano board is connected to SPI1.