msi-ec: add Cyborg 15 B2RW and MS-1606 backlight support

[ItsVaidas]

What changed

• add 15Q3EMS1.108 firmware support for Cyborg 15 B2RWEKG/B2RWGKG
• add a HID driver for the laptop's 0db0:1606 MSI MysticLight MS-1606 controller
• expose the controller as msi::kbd_backlight with levels 0 through 4
• suppress the non-functional EC keyboard-backlight interface on this firmware
• include the HID module in regular and DKMS installation paths

Why

On this generation, EC register 0xd3 is only a status mirror. Writes update
the register but do not change the physical keyboard. The keyboard lighting is
controlled by a dedicated USB HID device.

The MS-1606 does not provide a separate brightness command or useful RGB
readback. The driver therefore scales a configurable fixed RGB color in the
steady-effect packet. The default 255:50:0 color can be changed with the
color_red, color_green, and color_blue module parameters.

Validation

• tested all five brightness states on MSI Cyborg 15 B2RWGKG
• verified the MS-1606 HID report sequence against MSI Center's four-zone implementation
• built against 7.1.5-1-cachyos with Clang
• checkpatch.pl --strict: zero errors, warnings, or checks
• installed and exercised through DKMS and the Linux LED sysfs interface