Include modules for Chromebook Plus display

Samsung Chromebook Plus (v1) needs pwm_bl, rockchipdrm, pwm-cros-ec and panel-simple for the display to work. Booting and interacting with initramfs prompts works without these, it's just that messages aren't visible since the display/framebuffer is off/uninitialized.

This took a while because I was (and still am) confused as to how the console in initramfs works. From what I understand now, the device firmware normally provides a framebuffer and the drivers for that is already built-in (efifb, vesafb, vga16fb, fbcon), so nothing needs to be included in the initramfs. In my case the firmware doesn't provide that, so I need rockchipdrm to setup the framebuffer and the others are there to turn the display on. Please correct me if I'm wrong here.

I've tested this with my machine, but not with any others. I'm particularly worried about what /sys/class/graphics/* would include in systems with NVIDIA/AMD GPUs.