TI C2000 example: add standalone SHA-2 and SHA-3 examples

[dgarske]

Adds two small standalone hash examples to embedded/ti-c2000-f28p55x so the SHA-2 and SHA-3 call flow can be read in one file each, without wolf_main.c or the upstream test/benchmark harness.

What it adds

• Source/test_sha2.c (make SHA2=1) - SHA-224/256/384/512, SHA-512/224, SHA-512/256
• Source/test_sha3.c (make SHA3=1) - SHA3-224/256/384/512, SHAKE128, SHAKE256
• Source/c2000_board.c, Header/c2000_board.h - clocks, SCIA console and CPU Timer 0 for the two examples

Each example runs Init -> Update -> Final -> Free per variant on the FIPS 180-4 / FIPS 202 "abc" vector, a multi-Update streaming case, and a throughput loop through the generic wc_Hash* API.

Touches shared files

• Makefile - SHA2=1 / SHA3=1 build only that family's wolfCrypt source; combining them with each other or any other toggle is a build error
• Header/user_settings.h - WOLF_SHA2_EXAMPLE / WOLF_SHA3_EXAMPLE select one family, no RNG, no ML-DSA
• 28p55x_wolf_flash_lnk.cmd - the .TI.ramfunc entries for sha3.obj / wc_mldsa.obj are skipped when those objects are not built
• README.md - section on the two examples, noting that the default image's test.c / benchmark.c come from the wolfSSL tree

The default image and wolf_main.c are unchanged.

Hardware / test status

Validated on LAUNCHXL-F28P55X (XDS110, SCIA 115200 8N1): every KAT passes in both images and the throughput loop completes. The default image still builds.