powerpc: tqm834x: Fix build warnings in initdram()

powerpc: tqm834x: Fix build warnings in initdram()

With gcc 4.9, it produces the following warnings:

  CC      board/tqc/tqm834x/tqm834x.o
  board/tqc/tqm834x/tqm834x.c: In function 'initdram':
  board/tqc/tqm834x/tqm834x.c:325:12: warning: iteration 3u invokes undefined behavior [-Waggressive-loop-optimizations]
      (((base + size - 1) >> CSBNDS_EA_SHIFT) &
              ^
  board/tqc/tqm834x/tqm834x.c:80:2: note: containing loop
      for(cs = 0; cs < 4; ++cs) {
      ^

There is an integer overflow when cs = 3. To fix it, change
parameters of set_cs_bounds() to ulong.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>