Add TPM 2.0 resident server host keys for ECDSA and RSA

[aidangarske]

Description

• Lets a wolfSSH server use a host key stored in a TPM. The private key never enters RAM
• New API wolfSSH_CTX_UseTpmHostKey(ctx, dev, key) (replaces UsePrivateKey_buffer for TPM keys)
• KEX signature done in the TPM via wolfTPM; auto-advertises the matching host-key algorithm
• Supports ECDSA (P-256/384/521) and RSA (rsa-sha2-256)
• Echoserver -G option demonstrates the flow
• CI matrix: {rsa, ecc} × {ibmswtpm2, fwtpm} simulators
• README section added; no API breaks; clean with and without --enable-tpm

[dgarske]

Please double check our existing wolfTPM integration support and make sure this connects with it. I really like that you added wolfTPM fTPM support in the CI