Fix kernel unaligned access on sparc64

Update the SA_COPY_DATA macro to check if architecture supports
efficient unaligned memory accesses at compile time. Otherwise
fallback to using the sa_copy_data() function.

The kernel provided CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is
used to determine availability in kernel space. In user space
the x86_64, x86, powerpc, and sometimes arm architectures will
define the HAVE_EFFICIENT_UNALIGNED_ACCESS macro.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #7642
Closes #7684