enic: define constants for legacy interrupts offset

Use macro instead of function calls. These values are constant and will
not change.

Signed-off-by: Govindarajulu Varadarajan <govind.varadar@gmail.com>
Link: https://lore.kernel.org/r/20221018005804.188643-1-govind.varadar@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>