[PATCH v4 0/5] Add system timer driver for Mediatek SoCs

[Stanley Chu]

This patch adds a new driver for system timer on the Mediatek SoCs.

Changes since v3:
- Use the same binding style for both GPT and System Timer.
- Use timer_of.of_clk->period instead of private structure.
- Arrange patches to contain system timer changes in patch 5/5 only.

Changes since v2:
- Rename existed mtk_timer.c to timer-mediatek.c.
- Add system timer support into timer-mediatek.c instead of creating a new file.
- Use _gpt_ and _syst_ to identify different timers.
- Convert gpt driver to use timer_of.
- Fix system timer driver: irq flags.
- Fix bindings of both gpt and system timer.

Changes since v1:
- Use timer_of structure and APIs to make driver more clean.
- Remove unnecessary headers.
- Use fixed-clock.
- Fix indent.