fix(trng): avoid undefined behaviour in pack_entropy

When nbits is a multiple of the word size, the pack_entropy function
right shifts the mask by the type width, which is undefined. In
practice, th

fix(trng): avoid undefined behaviour in pack_entropy

When nbits is a multiple of the word size, the pack_entropy function
right shifts the mask by the type width, which is undefined. In
practice, the 64-bit shift compiles to a no-op and the implementation
depends on this behaviour, so this patch changes the function to skip
the masking if nbits is multiple of the word size.

Change-Id: I478b8102aae0a1d49182e7a8a55f70fd9438b9f9
Signed-off-by: Jamie Fox <jamiefox@google.com>

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refactor(trng): discarding the used entropy bits

This patch discards all the used entropy bits from the global memory
pool after being delivered to the requester (lower exception levels) by
overwrit

refactor(trng): discarding the used entropy bits

This patch discards all the used entropy bits from the global memory
pool after being delivered to the requester (lower exception levels) by
overwriting them with zeroes.
It effectively implements the requirement, as part of TRNG FW interface
listed at DEN0098 (section 1.2).
https://developer.arm.com/documentation/den0098/latest

Change-Id: I447cbccc1a8ad972418a3569c99f010189d4b2f6
Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>

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refactor(trng): cleanup the existing TRNG support

This patch adds the following changes to complete the existing
TRNG implementation:

1. Adds a feature specific scope for buildlog generation.
2. Up

refactor(trng): cleanup the existing TRNG support

This patch adds the following changes to complete the existing
TRNG implementation:

1. Adds a feature specific scope for buildlog generation.
2. Updates the docs on the build flag "TRNG_SUPPORT" and its values.
3. Makefile update and improves the existing comments at few sections
for better understanding of the underlying logic.

Change-Id: I3f72f0ccd5c94005a2df87158cf23199d2160d37
Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>

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