gcc5: Update to use gcc5

- Adds legacy toolchain for use in older edk2 projects, this is the only
  project using the pre 5.x toolchain for now
- Removes the bare metal toolchain
- qemu: Change the path for libraries for GCC5
- fvp: compiler changes for ARM-TF and EDK2
       Update libteec path in initramfs
- mtk: Toolchain and libteec path updates
- juno: Toolchain and libteec path updates

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>
Tested-by: Joakim Bech <joakim.bech@linaro.org> (QEMU, FVP, HiKey)
Tested-by: Pascal Brand <pascal.brand@linaro.org> (QEMU)
Tested-by: Pascal Brand <pascal.brand@linaro.org> (FVP)