powerpc/fadump: cleanup crash memory ranges support

Commit 1bd6a1c4 ("powerpc/fadump: handle crash memory ranges array
index overflow") changed crash memory ranges to a dynamic array that
is reallocated on-demand with krealloc(). The relevant header for this
call was not included. The kernel compiles though. But be cautious and
add the header anyway.

Also, memory allocation logic in fadump_add_crash_memory() takes care
of memory allocation for crash memory ranges in all scenarios. Drop
unnecessary memory allocation in fadump_setup_crash_memory_ranges().

Fixes: 1bd6a1c4 ("powerpc/fadump: handle crash memory ranges array index overflow")
Cc: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>