[UMD] Remove a couple of leftover usages of old soc descriptor API

[broskoTT]

Ticket

Related to #17002

Problem description

A follow up from removing .dram_cores in #17620 and removing eth_cores in #17642

Not sure if I made mistake during merging changes, or if these changes happened in the meantime. With this changes, tt_metal builds with this UMD change which is the ultimate goal: tenstorrent/tt-umd#509

What's changed

• Changed .dram_cores with .get_dram_cores()
• Changed .ethernet_cores with .get_cores(CoreType::ETH)

Checklist

All runs on brosko/umd_api_last_changes :

• All post-commit tests : https://github.com/tenstorrent/tt-metal/actions/runs/13548653822
• Blackhole post-commit tests : https://github.com/tenstorrent/tt-metal/actions/runs/13548656443
• (Single-card) Model perf tests : https://github.com/tenstorrent/tt-metal/actions/runs/13548658812
• (Single-card) Device perf regressions : https://github.com/tenstorrent/tt-metal/actions/runs/13548660915
• (T3K) T3000 unit tests : https://github.com/tenstorrent/tt-metal/actions/runs/13548663044
• (T3K) T3000 demo tests : https://github.com/tenstorrent/tt-metal/actions/runs/13548664896
• (TG) TG unit tests : https://github.com/tenstorrent/tt-metal/actions/runs/13548666720
• (TG) TG demo tests : https://github.com/tenstorrent/tt-metal/actions/runs/13548669182
• (TGG) TGG unit tests : https://github.com/tenstorrent/tt-metal/actions/runs/13548671739
• (TGG) TGG demo tests : https://github.com/tenstorrent/tt-metal/actions/runs/13548674558