config: update synopsys defconfigs

With this commit we update ARC defconfigs with the following:

  - "snps_axs101_defconfig" and "snps_axs103_defconfig":
     - bump linux kernel version to 4.7
     - set up host linux headers to 4.7
     - bump u-boot version to 2016.07

  - "snps_hs38_smp_vdk_defconfig":
     - bump linux kernel version to 4.7
     - set up host linux headers to 4.7

Also we delete "snps_hs38_vdk_defconfig" as we doesn't support
uni-processor HS38 configuration for vdk any longer.

Signed-off-by: Vlad Zakharov <vzakhar@synopsys.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>