x86/cpu/tsx: Define pr_fmt()

... so that all current and future pr_* statements in this file have the
proper prefix.

No functional changes.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: x86@kernel.org
Link: https://lkml.kernel.org/r/20191112221823.19677-2-bp@alien8.de