generic: enable dnsmasq ed25519 keys regardless of target

OpenWrt disabled ed25519 SSH keys for SMALL_FLASH targets back in 2020,
however this now affects ramips-mt76x8 targets.

ALways compile dnsmasq with ed25519 support. Without this patch,
previously working ed25519 keys would be unusable on said devices
without this patch.

Link: https://github.com/openwrt/openwrt/commit/d0f295837a03f7f52000ae6d395827bdde7996a4
Link: https://github.com/openwrt/openwrt/commit/fd46680966e9b9bc282b665282e2e6a22a27c26e



Signed-off-by: David Bauer <mail@david-bauer.net>