zephyr: riscv: use __rom_region_size for image size
zephyr: riscv: use __rom_region_size for image size

_image_rom_size was renamed to __rom_region_size in v2.7.  We
backported this to our v2.6 branches, so switch the name ahead of time
so we're prepared for the v2.7 uprev.

BUG=b:198824039
BRANCH=none
TEST=compile hayato EC with zephyr v2.7

Signed-off-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Change-Id: Iae6e7008d729f77cd66ed1a35e93001511d9cea8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3163562
Commit-Queue: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>
Reviewed-by: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec