ppc, arm: rework and enhance keymile-common.h

ppc, arm: rework and enhance keymile-common.h

Add:
  - introduce "bootrunner" environment variable
    This allows to execute consecutive different commands
    specified in the list "subbootcmd". If one command fails
    the command serie will stop.
  - introduce environment variable "develop", "ramfs" and "release"
    Each variable is one way to boot our linux. "develop" is for
    development purpose and boots the SW via NFS. "release" is for
    booting the linux image from flash, "ramfs" allows to load an SW
    image via tftp into ram and executes from there
  - introduce "addmem" variable, this command adds the used memory
    for linux to the bootargs
  - introduce "addvar" variable, this command adress for the /var
    directory to the kernel command line
  - introduce "setramfspram" and "setrootfsaddr" these calculation
    were done if "ramfs" was used (only for debugging)
  - introduce "tftpramfs" used for "ramfs" to load the image into
    RAM (only for debugging)
Remove unneeded stuff:
   - CONFIG_IO_MUXING is obsolete for keymile boards
   - CONFIG_KM_DEF_ENV_PRIVATE is also obsolete
   - define CONFIG_SYS_TEXT_BASE in board configs only

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
cc: Wolfgang Denk <wd@denx.de>
cc: Prafulla Wadaskar <prafulla@marvell.com>
cc: Valentin Longchamp <valentin.longchamp@keymile.com>
cc: Heiko Schocher <hs@denx.de>