[new uImage] Rename architecture specific bootm code files

Implementation of the do_bootm_linux() and other bootm helper routines is
architecture specific code. As such it resides in lib_<arch> directories
in files named <arch>_linux.c

This patch renames those files to a more clear and accurate
lib_<arch>/bootm.c form.

List of the renamed files:
   lib_arm/armlinux.c -> lib_arm/bootm.c
   lib_avr32/avr32_linux.c -> lib_avr32/bootm.c
   lib_blackfin/bf533_linux.c -> lib_blackfin/bootm.c
   lib_i386/i386_linux.c -> lib_i386/bootm.c
   lib_m68k/m68k_linux.c -> lib_m68k/bootm.c
   lib_microblaze/microblaze_linux.c -> lib_microblaze/bootm.c
   lib_mips/mips_linux.c -> lib_mips/bootm.c
   lib_nios/nios_linux.c -> lib_nios/bootm.c
   lib_nios2/nios_linux.c -> lib_nios2/bootm.c
   lib_ppc/ppc_linux.c -> lib_ppc/bootm.c
   lib_sh/sh_linux.c -> lib_sh/bootm.c

Signed-off-by: Marian Balakowicz <m8@semihalf.com>