kern/ieee1275/init/ppc64: Add support for alignment requirements

kern/ieee1275/init/ppc64: Add support for alignment requirements

Add support for memory alignment requirements and adjust a candidate
address to it before checking whether the block is large enough. This
must be done in this order since the alignment adjustment can make
a block smaller than what was requested.

None of the current callers has memory alignment requirements but the
ieee1275 loader for kernel and initrd will use it to convey them.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Pavithra Prakash <pavrampu@in.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Carolyn Scherrer <cpscherr@us.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Sourabh Jain <sourabhjain@linux.ibm.com>