[PARISC] Fix kernel panic in check_ivt

check_ivt had some seriously broken code wrt function pointers on
parisc64. Instead of referencing the hpmc code via a function pointer,
export symbols and reference it as a const array.

Thanks to jda for pointing out the broken 64-bit func ptr handling.

Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>