Add new example for HMAC SHA

[Akshay-Belsare]

Adds a new example demonstrating HMAC SHA algorithms:

• TA_ALGO_HMAC_SHA1

• TA_ALGO_HMAC_SHA224

• TA_ALGO_HMAC_SHA256

• TA_ALGO_HMAC_SHA384

• TA_ALGO_HMAC_SHA512

• TA_ALG_AES_CMAC

• Enabled runtime selection of the SHA algorithm by running
  optee_example_sha <string> <algo>.

• If no algorithm is specified, TA_ALGO_HMAC_SHA256 is used by default.

[jenswi-linaro]

Can this PR and #131 use the same TA?

[jenswi-linaro]

Hmm, so the pattern seems to be one TA per Linux user-space application.
Can the #131 also use the same user-space application?

[amey-raghatate]

Hi @jenswi-linaro, basic SHA and SHA HMAC use fundamentally different GlobalPlatform APIs and belong to distinct algorithm categories, making separate TAs the optimal approach. These algorithm families are different - basic SHA uses TEE_ALG_SHA* with TEE_DigestUpdate() and TEE_DigestDoFinal() APIs, while SHA HMAC uses TEE_ALG_HMAC_* with TEE_MACUpdate() and TEE_MACComputeFinal() APIs. Basic SHA algorithms are stateless, designed for hash-only operations that need no key material and are pure digest operations, whereas SHA HMAC algorithms are stateful with keys, require key objects and MAC operations for authentication. @jenswi-linaro Please advise if you have any suggestions regarding this this approach.

CC: @Akshay-Belsare

[jenswi-linaro]

@amey-raghatate, I'm well aware of the GP API. Combining the two apps should save a bit of common code.

[Akshay-Belsare]

@jenswi-linaro combined example PR #136 is raised.

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