Back RngLib with the hardware TRNG

[C-Prime90]

The SoC has a non-secure TRNG at 0xfe378000 that nothing was using. RngLib
resolved to BaseRngLibTimerLib — the performance counter, reporting
gEdkiiRngAlgorithmUnSafe — and that's what TlsDxe, Hash2DxeCrypto and
IScsiDxe link against, so HTTPS boot was seeded from a timer.
EFI_RNG_PROTOCOL was unaffected: RngDxe sorts an unsafe RngLib algorithm to
the end of its list and serves Raw from TF-A's SMCCC TRNG first.

It has to be a RngLib instance, not DxeRngLib — that depexes on
gEfiRngProtocolGuid, which RngDxe both produces and consumes RngLib for, so
RngDxe would wait on a protocol only it can install and never dispatch.

GetRngGuid reports gRk3588RngAlgorithmTrngV1Guid rather than
gEfiRngAlgorithmRaw, which is already taken by the SMCCC TRNG and would
advertise the same algorithm twice. EFI_RNG_PROTOCOL gains a second entry
and this block becomes its default. On fallback the library reports UnSafe
and RngDxe demotes it as before.

The version register is checked before anything else is touched, falling back
to the performance counter if it doesn't answer, so a board where the block
is unreachable behaves as it did before.

Verified on a PowerStation 6 over serial: Rk3588Rng: TRNG v1 ready. under
both RngDxe and TlsDxe, with RngDxe's unsafe-algorithm warning absent.
Enabled by default via RK3588_TRNG_ENABLE.

[mariobalanica]

It has to be a RngLib instance, not DxeRngLib — that depexes on
gEfiRngProtocolGuid, which RngDxe both produces and consumes RngLib for, so
RngDxe would wait on a protocol only it can install and never dispatch.

Right, but we don't have to link RngDxe against DxeRngLib. It can remain the BaseRngLibTimerLib instance, and for UEFI_DRIVERs (which TlsDxe & the others are), you can simply add RngLib|MdePkg/Library/DxeRngLib/DxeRngLib.inf to:

edk2-rk3588/edk2-rockchip/Silicon/Rockchip/Rockchip.dsc.inc

Line 322 in ef2d089

[LibraryClasses.common.UEFI_DRIVER]

which overrides the timer-based instance just for that driver type.

So we don't actually need a second driver here.

[mariobalanica]

be4d361

[C-Prime90]

Obsoleted by be4d361 — that covers the
UEFI_DRIVER consumers, and TF-A's rk3588_trng.c already drives the same
block at 0xfe378000, so a second instance buys nothing. Closing.