mediatek: Add mt7986 secure boot defconfig

Add secure boot and encrypted storage support for ATF.
Patches from MTK Secure Boot tarball:

• 0001_fix_atf_bl32_define.patch
• 0002_upgrade_BL31_xlat_lib_as_v2.patch
• 0003_drivers_auth_mbedtls_add_mbedtls_AES_options.patch
• 0004_add_mtk_secure_data_proc_data_sip_call.patch
• 0005_add_mtk_secure_data_get_key_sip_call.patch
• 0006_add_crypto_library_and_api.patch
• 0008_decrypt_roe-key_using_SEJ.patch
• 0009_add_HUID0_HUID1_efuse_field_in_mtk_efuse.c.patch
• 0011_add_locks_for_secure_data_SMC_calls.patch