We could maintain the static conversions for the !AArch64 Raspberry Pis, but I'm not sure it's worth it -- we'll traverse the platform list exactly once (of which there are only two for armv7), then every conversion there-after traverses the memory map listing (of which there are at-most two entries for these boards: sdram and peripheral space).
Detecting this at runtime is necessary for the AArch64 SOC, though, because there's no other way to discern the RPi3 from the RPi4, and the latter may have > 1GB RAM of which only the lowest 1GB is available to peripherals. This fixes DMA on the RPi4 enough that we can get read the sdcard almost to userland -- as soon as something attempts to write, the SDHCI controller puts the DMA channel on hold and starts timing out.