Build: Unify isolation level setting with TFM_ISOLATION_LEVEL

There is a CMake configuration "TFM_ISOLATION_LEVEL", which can also be
used as the CMake compile definition. To make the code easier to
maintain, remove current compile definition "TFM_LVL" and unify the
isolation level setting with "TFM_ISOLATION_LEVEL".

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I659744b470e8da6f14457094402e45cf77964406
37 files changed