Merge changes I6e4cd8b5,Id5086b3c,I070d62bb into integration

* changes:
fix(el3-runtime): allow RNDR access at EL3 even when RNG_TRAP is enabled
fix(smccc): don't panic on a feature availability

Merge changes I6e4cd8b5,Id5086b3c,I070d62bb into integration

* changes:
fix(el3-runtime): allow RNDR access at EL3 even when RNG_TRAP is enabled
fix(smccc): don't panic on a feature availability call with FEAT_RNG_TRAP
fix(bl1): use per-world context correctly

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fix(el3-runtime): allow RNDR access at EL3 even when RNG_TRAP is enabled

RNG_TRAP will also trap RNDR accesses at EL3 which we don't want as we
have no way to handle nested exceptions. Clear the tra

fix(el3-runtime): allow RNDR access at EL3 even when RNG_TRAP is enabled

RNG_TRAP will also trap RNDR accesses at EL3 which we don't want as we
have no way to handle nested exceptions. Clear the trap with root
context to always allow access at EL3.

Change-Id: I6e4cd8b5a7730f6ffbeed912d9301877d271110d
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>

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Merge changes from topic "fvp_trap_rng" into integration

* changes:
feat(fvp): emulate trapped RNDR
feat(el3-runtime): introduce system register trap handler

feat(fvp): emulate trapped RNDR

When a platform decides to use FEAT_RNG_TRAP, every RNDR or RNDRSS read
will trap into EL3. The platform can then emulate those instructions, by
either executing the

feat(fvp): emulate trapped RNDR

When a platform decides to use FEAT_RNG_TRAP, every RNDR or RNDRSS read
will trap into EL3. The platform can then emulate those instructions, by
either executing the real CPU instructions, potentially conditioning the
results, or use rate-limiting or filtering to protect the hardware
entropy pool. Another possiblitiy would be to use some platform specific
TRNG device to get entropy and returning this.

To demonstrate platform specific usage, add a demo implementation for the
FVP: It will execute the actual CPU instruction and just return the
result. This should serve as reference code to implement platform specific
policies.

We change the definition of read_rndr() and read_rndrrs() to use the
alternative sysreg encoding, so that all assemblers can handle that.

Add documentation about the new platform specific RNG handler function.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: Ibce817b3b06ad20129d15531b81402e3cc3e9a9e

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