I don't know what options you tried to build with, but I managed to build with the ROMLIB feature for the FVP platform. I will post everything I did here, hoping it will be of some use to you.
I used the following command to build:

MBEDTLS_DIR=<path_to_mbedtls> make ARM_ROTPK_LOCATION=devel_rsa CROSS_COMPILE=<path_to_cross_compiler(aarch64)> GENERATE_COT=1 PLAT=fvp ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem TRUSTED_BOARD_BOOT=1 USE_ROMLIB=1  DEBUG=1 fiptool all

The cross-compiler I used is GCC 8.3 for AArch64 ELF bare-metal target. You can get it from here:
https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-a/downloads