Add more linker debug.

- Show which executable is being linked, which linker config file is
  being read, and which section in it is being used with, enabled on
  $LD_DEBUG>=1.

- Show more info to follow the dlopen() process, enabled with "dlopen"
  in the debug.ld.xxx property.

Test: Flash, boot, and look at logcat after "adb shell setprop debug.ld.all dlopen"
Bug: 120430775
Change-Id: I5441c8ced26ec0e2f04620c3d2a1ae860b792154