[PATCH v6] Add optimized Makefile support for SoCFPGA handoff

[Sune Brian]

> currently. I also don't see that you tested this "make O=/tmp/somedir"
> (which is not the HANDOFF_PATH thing) and I expect it doesn't work there
> as it references ".config" and not "$(objdir)/.config".

Do you mean the handoff not generating?
For normal build it is still functioning, and with this config.mk
should also have
this trouble.

```
make prepare O=/tmp/test
HANDOFF_PATH=/media/sf_shared/loader/hps_isw_handoff/ddr3_5128x4_hps_0
make[1]: Entering directory '/tmp/test'
  Using /home/intel/u-boot as source for U-Boot
  GEN     Makefile
  UPD     include/generated/timestamp_autogenerated.h
[INFO] SOC family detected: cyclone5
[INFO] Using manually specified handoff folder:
/media/sf_shared/loader/hps_isw_handoff/ddr3_5128x4_hps_0
[INFO] Found hiof file:
/media/sf_shared/loader/hps_isw_handoff/ddr3_5128x4_hps_0/ddr3_5128x4_hps_0.hiof
[INFO] Running BSP generator...
python3: can't open file 'tools/cv_bsp_generator/cv_bsp_generator.py':
[Errno 2] No such file or directory
[WARN] BSP generator failed, continuing...
[DONE] SoCFPGA QTS handoff conversion complete.
make[1]: Leaving directory '/tmp/test'
```

Build capture.

```
make clean && make mrproper
  CLEAN   scripts/basic
  CLEAN   scripts/kconfig
  CLEAN   .config

make O=/tmp/test socfpga_cyclone5_defconfig
make[1]: Entering directory '/tmp/test'
  GEN     Makefile
#
# configuration written to .config
#
make[1]: Leaving directory '/tmp/test'

make O=/tmp/test
make[1]: Entering directory '/tmp/test'
  GEN     Makefile
scripts/kconfig/conf  --syncconfig Kconfig
  CFG     u-boot.cfg
  GEN     include/autoconf.mk
  GEN     include/autoconf.mk.dep
  CFG     spl/u-boot.cfg
  GEN     spl/include/autoconf.mk
  Using /home/intel/u-boot as source for U-Boot
  GEN     Makefile
  UPD     include/generated/version_autogenerated.h
  UPD     include/generated/timestamp_autogenerated.h
  UPD     include/generated/dt.h
  ENVC    include/generated/env.txt
  ENVP    include/generated/env.in
  ENVT    include/generated/environment.h
  HOSTCC  scripts/dtc/dtc.o
  HOSTCC  scripts/dtc/flattree.o


~/u-boot$ ls /tmp/test/
arch    disk     examples             lib       source      u-boot
 u-boot-dtb.bin  u-boot.map        u-boot-with-spl.sfp
boot    drivers  fs                   Makefile  spl         u-boot.bin
 u-boot-dtb.img  u-boot-nodtb.bin
cmd     dts      generated_defconfig  net       System.map  u-boot.cfg
 u-boot.img      u-boot.srec
common  env      include              scripts   tools       u-boot.dtb
 u-boot.lds      u-boot.sym
```

Brian