MFC r293892

sfxge: use correct register definitions for setting interrupt moderation on Medford

The only value which has changed is the number of rows
(ER_DZ_EVQ_TMR_REG_ROWS is 2048 vs 1024 for FR_BZ_TIMER_COMMAND_REGP0_ROWS)
but that isn't used, so this shouldn't change behaviour.

Submitted by: Mark Spender <mspender at solarflare.com>
Reviewed by: gnn
Sponsored by: Solarflare Communications, Inc.