powerpc/fadump: skip parameter area allocation when fadump is disabled

Fadump allocates memory to pass additional kernel command-line argument
to the fadump kernel. However, this allocation is not needed when fadump
is disabled. So avoid allocating memory for the additional parameter
area in such cases.

Fixes: f4892c68 ("powerpc/fadump: allocate memory for additional parameters early")
Reviewed-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Fixes: f4892c68 ("powerpc/fadump: allocate memory for additional  parameters early")
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20251008032934.262683-1-sourabhjain@linux.ibm.com