x86/sgx: Add helper to update SGX_LEPUBKEYHASHn MSRs

Add a helper to update SGX_LEPUBKEYHASHn MSRs.  SGX virtualization also
needs to update those MSRs based on guest's "virtual" SGX_LEPUBKEYHASHn
before EINIT from guest.

Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lkml.kernel.org/r/dfb7cd39d4dd62ea27703b64afdd8bccb579f623.1616136308.git.kai.huang@intel.com