FAPI: Improve the error message for self signed EK certificates. #2102

Job	Run time
coverity-test	0s
build-test (ubuntu-20.04, gcc)	4m 28s
scanbuild	6m 33s
test-coverage	5m 15s
build-test (ubuntu-20.04, clang)	4m 24s
test-fuzz	2m 30s
build-test (fedora-32, gcc)	4m 40s
build-test (fedora-32, clang)	4m 59s
test-mbedtls (ubuntu-20.04)	2m 48s
test-no-crypto-build	1m 23s
build-test (opensuse-leap, gcc)	4m 44s
test-tcti-config	14m 1s
test-mbedtls (ubuntu-22.04-mbedtls-3.1)	2m 41s
build-test (opensuse-leap, clang)	4m 37s
build-test (ubuntu-22.04, gcc)	4m 47s
build-test (ubuntu-22.04, clang)	4m 37s
build-test (alpine-3.15, gcc)	3m 55s
build-test (alpine-3.15, clang)	4m 48s
	1h 21m 10s

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