[foreign-memaccess+abi] RFR: Remove workarounds for issue surrounding upcalls and deoptimizations.

[Jorn Vernee]

Please review this patch which removes the (partial) workaround in aarch64 upcall code for spilling the receiver during a deopt. This has been properly fixed in the mainline by: https://github.com/openjdk/jdk/pull/6522 instead.

It also restores the lazy-customization behavior of upcalls which was removed to work around the same issue (originally added by: https://github.com/openjdk/panama-foreign/pull/553).

Thanks,
Jorn

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Commit messages:
 - Remove deopt spill space from aarch64 as well
 - Re-drop ensureCustomized

Changes: https://git.openjdk.java.net/panama-foreign/pull/625/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=625&range=00
  Stats: 24 lines in 4 files changed: 0 ins; 22 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/625.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/625/head:pull/625

PR: https://git.openjdk.java.net/panama-foreign/pull/625