Update the mbed TLS submodule to the 3.6.6 release and bump
MBEDTLS_CONFIG_VERSION in default_mbedtls_config.h so the
Trusted Firmware-A configuration matches the imported version.
Change-Id: I9f90eecfbce203a89c61e864ef3f85677efad1c4
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
(cherry picked from commit 28aa61ddc0)