Separate sanity checks for each command

Separated the sanity checks to be specific for each command entered, avoiding
unnecessary calls in case of wrong input. Introduced two new functions:
tc_env_init and tc_demo_app_init. The tc_env_init function is responsible for
the basic sanity checks required for all commands, while the tc_demo_app_init
function includes additional checks specific to running the TC demo app.

Signed-off-by: Ahmed Genidi <ahmed.genidi@arm.com>