MAINTAINERS: adjust to trusted keys subsystem creation

Commit 47f9c279 ("KEYS: trusted: Create trusted keys subsystem")
renamed trusted.h to trusted_tpm.h in include/keys/, and moved trusted.c
to trusted-keys/trusted_tpm1.c in security/keys/.

Since then, ./scripts/get_maintainer.pl --self-test complains:

  warning: no file matches F: security/keys/trusted.c
  warning: no file matches F: include/keys/trusted.h

Rectify the KEYS-TRUSTED entry in MAINTAINERS now and ensure that all
files in security/keys/trusted-keys/ are identified as part of
KEYS-TRUSTED.

Co-developed-by: Sebastian Duda <sebastian.duda@fau.de>
Signed-off-by: Sebastian Duda <sebastian.duda@fau.de>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>