powerpc/akebono: Fix unmet dependency errors

The AKEBONO config has various selects under it, including some with
user-selectable dependencies, which means those dependencies can be
disabled. This leads to warnings from Kconfig.

This can be seen with eg:

  $ make allnoconfig
  $ ./scripts/config --file build~/.config -k -e CONFIG_44x -k -e CONFIG_PPC_47x -e CONFIG_AKEBONO
  $ make olddefconfig

  WARNING: unmet direct dependencies detected for ATA
    Depends on [n]: HAS_IOMEM [=y] && BLOCK [=n]
    Selected by [y]:
    - AKEBONO [=y] && PPC_47x [=y]

  WARNING: unmet direct dependencies detected for NETDEVICES
    Depends on [n]: NET [=n]
    Selected by [y]:
    - AKEBONO [=y] && PPC_47x [=y]

  WARNING: unmet direct dependencies detected for ETHERNET
    Depends on [n]: NETDEVICES [=y] && NET [=n]
    Selected by [y]:
    - AKEBONO [=y] && PPC_47x [=y]

  WARNING: unmet direct dependencies detected for MMC_SDHCI
    Depends on [n]: MMC [=n] && HAS_DMA [=y]
    Selected by [y]:
    - AKEBONO [=y] && PPC_47x [=y]

  WARNING: unmet direct dependencies detected for MMC_SDHCI_PLTFM
    Depends on [n]: MMC [=n] && MMC_SDHCI [=y]
    Selected by [y]:
    - AKEBONO [=y] && PPC_47x [=y]

The problem is that AKEBONO is using select to enable things that are
not true dependencies, but rather things you probably want enabled in
an AKEBONO kernel. That is what a defconfig is for.

So drop those selects and instead move those symbols into the
defconfig. This fixes all the kconfig warnings, and the result of make
44x/akebono_defconfig is the same before and after the patch.

Reported-by: Yury Norov <yury.norov@gmail.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20210201012503.940145-1-mpe@ellerman.id.au