m32r: Move defconfig files to arch/m32r/configs/

Change defconfig file's location from arch/m32r/{platform}/defconfig*
to arch/m32r/configs/{platform}_defconfig.

Applying this patch, we can use defconfig file for each m32r platform
easily, like other architectures.

  ex. Setup defconfig for cross-building
    $ make ARCH=m32r CROSS_COMPILE=m32r-linux-gnu- {platform}_defconfig.

  platform    defconfig                 Note
 ----------  ----------------------    ---------------------------
  m32104ut    m32104ut_defconfig        MMU-less
  m32700ut    m32700ut.smp_defconfig    SMP
  m32700ut    m32700ut.up_defconfig     UP
  mappi       mappi.smp_defconfig       SMP
  mappi       mappi.up_defconfig        UP
  mappi       mappi.nommu_defconfig     MMU-less
  mappi2      mappi2.opsp_defconfig     FPGA env. (CPU Core: OPSP)
  mappi2      mappi2.vdec2_defconfig    FPGA env. (CPU Core: VDEC2)
  mappi3      imappi3.smp_defconfig     SMP
  oaks32r     oaks32r_defconfig         MMU-less
  opsput      opsput_defconfig          UP

Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>