Get EC ROM size

[crawfxrd]

addw4 switched to the 256 KiB variant of the chip.

Get the real ROM size instead of hard-coding it to 128 KiB

firmware-update/src/app/ec.rs

Lines 317 to 325 in ecd5fcf

	fn rom_size(&self) -> usize {
	128 * 1024
	}
	fn block_size(&self) -> usize {
	64 * 1024
	}
	fn page_size(&self) -> usize {
	256
	}