Rework arithmetic operations in Test Secure Payload ...

This patch reworks the service provided by the TSP to perform common
arithmetic operations on a set of arguments provided by the non-secure
world. For a addition, division, subtraction & multiplication operation
requested on two arguments in x0 and x1 the steps are:

1. TSPD saves the non-secure context and passes the operation and its
   arguments to the TSP.

2. TSP asks the TSPD to return the same arguments once again. This
   exercises an additional SMC path.

3. TSP now has two copies of both x0 and x1. It performs the operation
   on the corresponding copies i.e. in case of addition it returns x0+x0
   and x1+x1.

4. TSPD receives the result, saves the secure context, restores the
   non-secure context and passes the result back to the non-secure
   client.

Change-Id: I6eebfa2ae0a6f28b1d2e11a31f575c7a4b96724b
Co-authored-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

Add Test Secure Payload (BL3-2) image ...

This patch adds a simple TSP as the BL3-2 image. The secure payload
executes in S-EL1. It paves the way for the addition of the TSP
dispatcher runtime service to BL3-1. The TSP and the dispatcher service
will serve as an example of the runtime firmware's ability to toggle
execution between the non-secure and secure states in response to SMC
request from the non-secure state.  The TSP will be replaced by a
Trusted OS in a real system.

The TSP also exports a set of handlers which should be called in
response to a PSCI power management event e.g a cpu being suspended or
turned off. For now it runs out of Secure DRAM on the ARM FVP port and
will be moved to Secure SRAM later. The default translation table setup
code assumes that the caller is executing out of secure SRAM. Hence the
TSP exports its own translation table setup function.

The TSP only services Fast SMCs, is non-reentrant and non-interruptible.
It does arithmetic operations on two sets of four operands, one set
supplied by the non-secure client, and the other supplied by the TSP
dispatcher in EL3. It returns the result according to the Secure Monitor
Calling convention standard.

This TSP has two functional entry points:

- An initial, one-time entry point through which the TSP is initialized
  and prepares for receiving further requests from secure
  monitor/dispatcher

- A fast SMC service entry point through which the TSP dispatcher
  requests secure services on behalf of the non-secure client

Change-Id: I24377df53399307e2560a025eb2c82ce98ab3931
Co-authored-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>