riscv: dts: spacemit: add pwm14_1 pinctrl setting

riscv: dts: spacemit: add pwm14_1 pinctrl setting

This patch adds the option 1 (hence the name pwm14_1) pinctrl
configuration for PWM14 on the SpacemiT K1 SoC.

PWM14 option 1 is used for PWM-based backlight control on MIPI displays.
This configuration is present on all existing K1 development boards,
such as the Banana Pi BPI-F3 and the Milk-V Jupiter.

For reference, a more complete list of PWM0-PWM19 pinctrl configurations
including all options can be found in [1].

Note: Since the corresponding functionality for other pins is not yet
in use or ready for upstreaming, this patch includes only the pwm14_1
setting.

[1] https://lore.kernel.org/all/20250411131423.3802611-7-guodong@riscstar.com/

Signed-off-by: Guodong Xu <guodong@riscstar.com>
Link: https://lore.kernel.org/r/20250429085048.1310409-5-guodong@riscstar.com
Signed-off-by: Yixun Lan <dlan@gentoo.org>