board: sifive: spl: Initialized the PWM setting in the SPL stage

board: sifive: spl: Initialized the PWM setting in the SPL stage

LEDs and multiple fans can be controlled by SPL. This patch ensures
that all fans have been enabled in the SPL stage. In addition, the
LED's color will be set to yellow.

Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Co-developed-by: Nylon Chen <nylon.chen@sifive.com>
Signed-off-by: Nylon Chen <nylon.chen@sifive.com>
Co-developed-by: Zong Li <zong.li@sifve.com>
Signed-off-by: Zong Li <zong.li@sifve.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>