powerpc/crash: use generic APIs to locate memory hole for kdump

On PowerPC, the memory reserved for the crashkernel can contain components
like RTAS, TCE, OPAL, etc., which should be avoided when loading kexec
segments into crashkernel memory.  Due to these special components,
PowerPC has its own set of APIs to locate holes in the crashkernel memory
for loading kexec segments for kdump.  However, for loading kexec segments
in the kexec case, PowerPC already uses generic APIs to locate holes.

The previous patch in this series, titled "crash: Let arch decide usable
memory range in reserved area," introduced arch-specific hook to handle
such special regions in the crashkernel area.  So, switch PowerPC to use
the generic APIs to locate memory holes for kdump and remove the redundant
PowerPC-specific APIs.

Link: https://lkml.kernel.org/r/20250131113830.925179-5-sourabhjain@linux.ibm.com


Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Cc: Baoquan he <bhe@redhat.com>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>