Heltec Vision Master E213: enable 32768hz crystal osc for rtc

[t-miura]

This enables onboard 32768Hz crystal oscillator available on Heltec Vision Master E213,
makes on-chip RTC less drifty and more reliable.

while it may not the best compared to a dedicated RTC module,
but still better than relying on drifty internal LC osc.

Exisistence of the crystal has been confirmed both on Heltec's page and schematics (https://heltec.org/project/vision-master-e213/) and on actual board itself.

Confirmed working on my own E213 board: RTC is working as excpected.

🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • Heltec (Lora32) V3
  • LilyGo T-Deck
  • LilyGo T-Beam
  • RAK WisBlock 4631
  • Seeed Studio T-1000E tracker card
  • Other (please specify below)
    • Heltec Vision Master E213

As a sidenote, the Heltec Vision Master E290 which is similar to this, has no 32kHz crystal,
so we can't get better clock on E290, unfortunately.
while i'm trying to utlize better internal OSC that's available on ESP32 families: 8MD256, but it's still in progress...

hope this small change will make E213 users' Meshtastic life little bit better!

[CLAassistant]

All committers have signed the CLA.

[github-actions]

@t-miura, Welcome to Meshtastic!

Thanks for opening your first pull request. We really appreciate it.

We discuss work as a team in discord, please join us in the #firmware channel.
There's a big backlog of patches at the moment. If you have time,
please help us with some code review and testing of other PRs!

Welcome to the team 😄

[github-actions]

Firmware Size Report

21 targets | vs develop: 21 increased, net +38,512 (+37.6 KB)

Target	Size	vs develop
station-g3	2,210,048	📈 +3,296 (+3.2 KB)
heltec-v3	2,208,640	📈 +3,216 (+3.1 KB)
station-g2	2,218,672	📈 +2,544 (+2.5 KB)
t-eth-elite	2,435,456	📈 +2,352 (+2.3 KB)
seeed-xiao-s3	2,218,752	📈 +2,304 (+2.2 KB)

Show 16 more target(s)

Target	Size	vs develop
rak3312	2,214,784	📈 +2,272 (+2.2 KB)
t-deck-tft	3,754,320	📈 +2,144 (+2.1 KB)
rak11200	1,804,112	📈 +2,112 (+2.1 KB)
pico2w	1,178,768	📈 +2,060 (+2.0 KB)
picow	1,197,280	📈 +2,040 (+2.0 KB)
seeed_xiao_rp2350	728,392	📈 +1,912 (+1.9 KB)
pico	737,360	📈 +1,896 (+1.9 KB)
pico2	730,232	📈 +1,896 (+1.9 KB)
rak11310	759,944	📈 +1,896 (+1.9 KB)
seeed_xiao_rp2040	735,560	📈 +1,896 (+1.9 KB)
heltec-vision-master-e213-inkhud	2,170,768	📈 +1,184 (+1.2 KB)
tlora-c6	2,316,096	📈 +912
heltec-ht62-esp32c3-sx1262	2,082,384	📈 +864
elecrow-adv-35-tft	3,362,320	📈 +768
wio-e5	232,404	📈 +488
rak3172	180,040	📈 +460

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Updated for 27fd63a