refactor(rpi3): move mbedtls helper to common code

In order to support measured boot we need plat_get_mbedtls_heap,
this function currently resides in rpi3_trusted_boot.c, but we do
not need trusted board boot to use measured boot, so moving this
to common code removes the need to compile rpi3_trusted_boot.c

Change-Id: I6ac6dfa8c540e456d7cb6932098c921907ad086a
Signed-off-by: Tushar Khandelwal <tushar.khandelwal@arm.com>
Signed-off-by: Abhi Singh <abhi.singh@arm.com>
2 files changed