RFR: 8155100: AArch64: Relax alignment requirement for byte_map_base

[Andrew Haley]

AArch64 expects the card table base to be page aligned, and asserts
that.  Unfortunately (because asserts are compiled out in release
code) if this assumption is ever violated in production code we won't
see it. Instead, we will see mysterious segfaults.

We have seen this fail in OpenJDK 7.

It makes more sense to allow the base to be unaligned.

http://cr.openjdk.java.net/~aph/8155100/hotspot.changeset

Andrew.