microblaze: Remove unneeded data section adding from DTB

DTB is added to rodata section:
  [ 2] .rodata           PROGBITS        84c5b60c 05c60c 00c618 00   A
0   0  4
  [ 3] .dtb.init.rodata  PROGBITS        84c67c30 068c30 003c80 00   A
0   0 16
  [ 4] .rela.dyn         RELA            84c6b8b0 06c8b0 000534 0c   A
0   0  4
  [ 5] .data             PROGBITS        84c6bde4 06cde4 001536 00  WA
0   0 16

Signed-off-by: Michal Simek <michal.simek@xilinx.com>