libc: Adapt to TFTF

Add support for functions used in TFTF but not in TF-A.

Replaced calls to plat_panic_handler with calls to panic, since there is no
implementation of the former in TFTF.

Change-Id: Ic10de2c6e749db97b932cd7ffbb6067b5befe914
Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>
10 files changed