docs: document DCP-backed trusted keys kernel params

Document the kernel parameters trusted.dcp_use_otp_key
and trusted.dcp_skip_zk_test for DCP-backed trusted keys.

Co-developed-by: Richard Weinberger <[e-mail]>
Signed-off-by: Richard Weinberger <[e-mail]>
Co-developed-by: David Oberhollenzer <[e-mail]>
Signed-off-by: David Oberhollenzer <[e-mail]>
Signed-off-by: David Gstir <[e-mail]>
Reviewed-by: Jarkko Sakkinen <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>

Documentation/admin-guide/kernel-parameters.txt

···
 			- "tpm"
 			- "tee"
 			- "caam"
+			- "dcp"
 			If not specified then it defaults to iterating through
 			the trust source list starting with TPM and assigns the
 			first trust source as a backend which is initialized
···
 			- "default"
 			If not specified, "default" is used. In this case,
 			the RNG's choice is left to each individual trust source.
+
+	trusted.dcp_use_otp_key
+			This is intended to be used in combination with
+			trusted.source=dcp and will select the DCP OTP key
+			instead of the DCP UNIQUE key blob encryption.
+
+	trusted.dcp_skip_zk_test
+			This is intended to be used in combination with
+			trusted.source=dcp and will disable the check if the
+			blob key is all zeros. This is helpful for situations where
+			having this key zero'ed is acceptable. E.g. in testing
+			scenarios.
 
 	tsc=		Disable clocksource stability checks for TSC.
 			Format: <string>