Fix FIPS v6 or older build with crypto callbacks and SHA512

[dgarske]

Description

Commit 9cbc3f9 added a size_t digestSz parameter to
wc_CryptoCb_Sha512Hash (to dispatch SHA-512/224 and SHA-512/256 to
variant-specific provider callbacks). The live sha512.c was updated to the
5-arg call, but in a FIPS build sha512.c is a frozen snapshot pulled from a
tag by fips-check.sh, while cryptocb.c/.h live outside the FIPS boundary
and ship the latest signature. For FIPS v6 and earlier the snapshot still calls
the old 4-arg API, so the build fails with:

sha512.c: error: too few arguments to function 'wc_CryptoCb_Sha512Hash'

(reported on --enable-fips=v5, e.g. wolfTPM builds).

This conditionally drops the digestSz parameter from the declaration and
definition under defined(HAVE_FIPS) && FIPS_VERSION_LT(7,0), with a shimmed
digestSz = WC_SHA512_DIGEST_SIZE local so the single shared body behaves
identically to the pre-9cbc3f97 4-arg function. No sha512.c change; the public
wc_CryptoInfo.hash struct is untouched, so callback providers (wolfTPM, HSMs)
need no changes.

Fixes ZD21902 and ZD21780

Testing

FIPS_VERSION_LT(7,0) is the boundary, verified against the snapshot tags in
fips-check.sh and the version assignments in configure.ac:

FIPS option	version	sha512.c source	API
v5 / cert4718	5.2.1	v5.2.1-stable (frozen)	4-arg
v5-RC12	5.2.0.1	WCv5.0-RC12 (frozen)	4-arg
v6 / wolfentropy	6.0	WCv6.0.0-RC5 (frozen)	4-arg
ready / dev	8.0	master (not overwritten)	5-arg
v7 (future)	7.0	snapshot picks up new sha512.c	5-arg

The tagged sha512.c for v5.2.1, RC12, and v6.0.0-RC5 were each confirmed to
call the 4-arg form; ready/dev leave sha512.c as live master (5-arg) and
report version 8, so they fall on the new-API side without special handling.

• Non-FIPS cryptocb.c compiles clean with WOLF_CRYPTO_CB + WOLFSSL_SHA512.
• Preprocessor expansion verified: non-FIPS -> 5 args, FIPS v5/v6 -> 4 args,
  FIPS v7 / ready / dev -> 5 args.

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• gcc-arm-cortex-m4
• gcc-arm-cortex-m4-baremetal
• gcc-arm-cortex-m4-min-ecc
• gcc-arm-cortex-m4-tls12