(kernel-rolling) input: phytium-keypad: Add Phytium keypad driver

[MingcongBai]

Picked and rebased from #201.

From original pull request:

This patch adds support for Phytium keypad controller driver on Phytium SoCs.

Builds tested

• amd64
• arm64
• loong64

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This is the kernel module for the PHYTIUM Keypad Port. It provides a
keyboard-like input device that can be used with the Linux kernel's input
system. The input device is based on a matrix keypad, which is a popular
embedded input device due its small size, low power consumption, and
easily accessible keys.

The module uses the Linux kernel's input system, which is responsible for
handling input events from various types of input devices. The input
system provides a common API for handling keyboard-like input events
and other types of input events as well.

Here is a brief overview of the module's main features:

1. It initializes the keypad controller and sets up the necessary hardware
   registers.

2. It configures the keypad controller to generate interrupts for key presses
   and releases.

3. It scans the keypad matrix and returns the new state in the
   matrix_volatile_state array.

4. It compares the new state with the stable state stored in
   matrix_stable_state and fires events if changes are detected.

5. It schedules a rescan in attempt to detect multiple key presses and
   enables the KRI interrupt to react quickly to key release events.

6. It handles the keypad interrupt and processes the key presses and
   releases accordingly.

7. It configures the input device and sets up the necessary hardware
   registers.

8. It registers the input device with the Linux kernel's input system.

9. It sets up the device to wake up from a sleep state if necessary.

10. It provides a platform driver for use with the Linux kernel's device
    framework.

The module is designed to be used with the Linux kernel and can be built
and loaded as a kernel module. It is also designed to be easily adapted
to different keypad controller hardware and configurations.