arm64: defconfig: updates for 4.6

A few defconfig updates got dropped on the floor during the merge window,
so I've rounded up the remainder here:

  * Fix duplicate definition of MMC_BLOCK_MINORS and bump to 32 for
    msm8916

  * CPUFreq support for the Juno platform, using the MHU/SCPI interface

  * Removal of the default command line, which assumed a console called
    ttyAMA0

  * Bits and pieces for the Hi6220 (96Boards HiKey)

Signed-off-by: Will Deacon <will.deacon@arm.com>