powerpc/fadump: pass additional parameters when fadump is active

Append the additional parameters passed/set in the dedicated parameter
area (RTAS_FADUMP_PARAM_AREA) to bootargs in fadump capture kernel.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240509115755.519982-4-hbathini@linux.ibm.com