Rework incorrect use of assert() and panic() in codebase

Assert a valid security state using the macro sec_state_is_valid().
Replace assert() with panic() in those cases that might arise
because of runtime errors and not programming errors.
Replace panic() with assert() in those cases that might arise
because of programming errors.

Fixes ARM-software/tf-issues#96

Change-Id: I51e9ef0439fd5ff5e0edfef49050b69804bf14d5
Merge pull request #177 from jcastillo-arm/jc/tf-issues/096

Rework incorrect use of assert() and panic() in codebase
Rework the TSPD setup code

There is no mechanism which allows the TSPD to specify what SPSR to
use when entering BL3-2 instead of BL3-3. This patch divides the
responsibility between tspd_setup() and tspd_init() for initializing
the TSPD and TSP to support the alternate BL3-2 initialization flow
where BL3-1 handsover control to BL3-2 instead of BL3-3.
SPSR generated by TSPD for TSP is preserved due the new division of
labour which fixes #174.

This patch also moves the cpu_context initialization code from
tspd_setup() to tspd_init() immediately before entering the TSP.
Instead tspd_setup() updates the BL3-2 entrypoint info structure
with the state required for initializing the TSP later.

Fixes  ARM-software/TF-issues#174

Change-Id: Ida0a8a48d466c71d5b07b8c7f2af169b73f96940
Support asynchronous method for BL3-2 initialization

This patch adds support for BL3-2 initialization by asynchronous
method where BL3-1 transfers control to BL3-2 using world switch.
After BL3-2 initialization, it transfers control to BL3-3 via SPD
service handler. The SPD service handler initializes the CPU context
to BL3-3 entrypoint depending on the return function indentifier from
TSP initialization.

Fixes ARM-software/TF-issues#184

Change-Id: I7b135c2ceeb356d3bb5b6a287932e96ac67c7a34