lib: utils/timer: Add Andes fdt timer support

Since we can get the PLMT base address and timer frequency from
device tree, move plmt timer device to fdt timer framework.

dts example (Quad-core AX45MP):

  cpus {
      ...
      timebase-frequency = <0x3938700>;
      ...
  }
  soc {
      ...
      plmt0@e6000000 {
          compatible = "andestech,plmt0";
          reg = <0x00 0xe6000000 0x00 0x100000>;
          interrupts-extended = <&cpu0_intc 0x07
                                 &cpu1_intc 0x07
                                 &cpu2_intc 0x07
                                 &cpu3_intc 0x07>;
      };
      ...
  }

Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
Reviewed-by: Anup Patel <anup@brainfault.org>