Drop linker-generated array creation when CONFIG_CMDLINE is disabled

Linker generated array entry is not needed when the command line is
disabled. Remove this code in that case.

This is required as the commit 80a48dd4
breaks the linking stage when CONFIG_CMDLINE=n:

..
  LDS     u-boot.lds
  LD      u-boot
u-boot contains unexpected relocations: R_ARM_NONE
R_ARM_RELATIVE
make: *** [Makefile:1775: checkarmreloc] Error 1

Signed-off-by: Andrej Rosano <andrej.rosano@f-secure.com>