SecurityPkg: RngDxe: Remove incorrect limitation on GetRng

Removed from gEfiRngAlgorithmRaw an incorrect assumption that
Raw cannot return less than 256 bits. The DRNG Algorithms
should always use a 256 bit seed as per nist standards
however a caller is free to request less than 256 bits.
>
>     //
>    // When a DRBG is used on the output of a entropy source,
>    // its security level must be at least 256 bits according to UEFI
Spec.
>    //
>    if (RNGValueLength < 32) {
>      return EFI_INVALID_PARAMETER;
>    }
>

AARCH64 platforms do not have this limitation and this brings both
implementations into alignment with each other and the spec.

Cc: Jiewen Yao <[email protected]>

Signed-off-by: Doug Flick [MSFT] <[email protected]>
Reviewed-by: Ard Biesheuvel <[email protected]>

SecurityPkg/RandomNumberGenerator/RngDxe/Rand/RngDxe.c

@@ -116,14 +116,6 @@ RngGetRNG (
   // The "raw" algorithm is intended to provide entropy directly
   //
   if (CompareGuid (RNGAlgorithm, &gEfiRngAlgorithmRaw)) {
-    //
-    // When a DRBG is used on the output of a entropy source,
-    // its security level must be at least 256 bits according to UEFI Spec.
-    //
-    if (RNGValueLength < 32) {
-      return EFI_INVALID_PARAMETER;
-    }
-
     Status = GenerateEntropy (RNGValueLength, RNGValue);
     return Status;
   }