dt-bindings: timer: Use defines instead of numbers in Exynos MCT examples

Make the examples in Exynos Multi Core Timer bindings more readable and
bring them closer to real DTS by using defines for interrupt flags.
Fix also GIC interrupt type in example for Exynos4412 (from SPI to PPI).

Suggested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>