efi_loader: fix efi_tcg2_hash_log_extend_event() parameter check

TCG EFI Protocol Specification defines that PCRIndex parameter
passed from caller must be 0 to 23.
TPM2_MAX_PCRS is currently used to check the range of PCRIndex,
but TPM2_MAX_PCRS is tpm2 device dependent and may have larger value.
This commit newly adds EFI_TCG2_MAX_PCR_INDEX macro, it is used to
check the range of PCRIndex parameter.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Acked-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>