drivers: intc: plic: support trigger type by default and hardcode offset

Removing the edge-trigger Kconfig as it is supported by default
in the RISCV PLIC specifications.

Define the edge-trigger register offset in the driver instead
of retrieving the value from devicetree as it is not something
configurable. The value 0x1080 is defined in Andes & Telink
datasheets.

Updated build_all testcase.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>