arm64: dts: ls208xa: use defines for timer interrupts

arm64: dts: ls208xa: use defines for timer interrupts

Replace hard-coded interrupt parts (GIC, flags) with standard defines
for readability.  No changes in resulting DTBs.  The comment was saying
interrupt was active low, but the actual used value was active high, so
assume that the code, not the comment, is correct.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>