parisc: Increase initial kernel mapping size

Increase the initial kernel default page mapping size for 64-bit kernels to
64 MB and for 32-bit kernels to 32 MB.

Due to the additional support of ftrace, tracepoint and huge pages the kernel
size can exceed the sizes we used up to now.

Cc: stable@vger.kernel.org # 4.4+
Signed-off-by: Helge Deller <deller@gmx.de>