Fix hotspot/test/runtime/Metaspace/MaxMetaspaceSizeTest.java in 8u

It was discovered [1] that following test is always skipped in 8u:
hotspot/test/runtime/Metaspace/MaxMetaspaceSizeTest.java

Test comes from JDK-8087291 [2] backport. Test is for 64-bit JDK only and uses following jtreg tag to test that:
@requires vm.bits == "64"

However vm.bits is not supported on 8u, where condition evaluates as always false, which results in test being skipped on all systems.

Fix:
Fixed by doing explicit check in test instead of using jtreg tag.

Testing:
Tested using github actions as test is part of hotspot/tier1.

[1] https://github.com/openjdk/jdk8u-dev/pull/182#discussion_r1024395333
[2] https://bugs.openjdk.org/browse/JDK-8087291