tpm: Enable TCG_TPM2_HMAC by default only for X86_64

Given the not fully root caused performance issues on non-x86 platforms,
enable the feature by default only for x86-64. That is the platform it
brings the most value and has gone most of the QA. Can be reconsidered
later and can be obviously opt-in enabled too on any arch.

Link: https://lore.kernel.org/linux-integrity/bf67346ef623ff3c452c4f968b7d900911e250c3.camel@gmail.com/#tSigned-off-by: Jarkko Sakkinen <jarkko@kernel.org>

drivers/char/tpm/Kconfig

@@ -29,7 +29,7 @@ if TCG_TPM
 
 config TCG_TPM2_HMAC
 	bool "Use HMAC and encrypted transactions on the TPM bus"
-	default y
+	default X86_64
 	select CRYPTO_ECDH
 	select CRYPTO_LIB_AESCFB
 	select CRYPTO_LIB_SHA256