yeah, you can either do baremetal arm under the official firmware (quad-core arm, up to 1.8ghz depending on the model)

or you can do baremetal VPU and skip the firmware entirely 500mhz dual-core VPU 128kb of L2 cache for both code and data if you want dram, you need the ram drivers (only present for the VC4 line, pi0-pi3) you could optionally rely on 1 closed stage to bring ram up, and do baremetal VPU from the start(4).elf to avoid the dram init sequence

and if you build upon rpi-open-firmware, you could get all 6 cores baremetal, running custom code