Build: Add error when bad options are given

When either of the two required input paramters (CMAKE_TOOLCHAIN_FILE
and TFM_PLATFORM) are given, validate that they are sane values and
output a reasonable error message if they are not.

Change-Id: Ie3a93ffed331e5ed66483f0b22c7875db469700c
Signed-off-by: Raef Coles <raef.coles@arm.com>
4 files changed