RFR: 8302070: Factor null-check into load_klass() calls

[Roman Kennke]

In several asm routines, a pattern like the following can be found:

        __ null_check(obj, oopDesc::klass_offset_in_bytes());
        __ load_klass(klass, obj, tmp);

The null-check logically belongs into load_klass(), though. This becomes apparent in Lilliput, where the klass-offset is different, depending on whether or not Lilliput is enabled.

Testing:
 - [x] tier1 x86_64
 - [x] tier1 aarch64

-------------

Commit messages:
 - ARM fix
 - S390 fixes
 - PPC fixes
 - ARM fixes
 - S390 parts
 - RISCV parts
 - PPC parts
 - ARM parts
 - AArch64
 - 8302070: Factor null-check into load_klass() calls

Changes: https://git.openjdk.org/jdk/pull/12473/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12473&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302070
  Stats: 89 lines in 28 files changed: 41 ins; 25 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/12473.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12473/head:pull/12473

PR: https://git.openjdk.org/jdk/pull/12473