parisc: Report trap type as human readable string

When faulting on some trap, the kernel currently reports in dmesg:

 do_page_fault() command='perl' type=6 address=0xbe400403 in libcrypt-2.24.so[f9086000+9000]
 vm_start = 0x00922000, vm_end = 0x00aed000

With this change the trap type additionally gets reported as human readable
string which makes it simpler to recognize the type of problem:

 do_page_fault() command='perl' type=6 address=0xbe400403 in libcrypt-2.24.so[f9086000+9000]
 trap #6: Instruction TLB miss fault, vm_start = 0x00922000, vm_end = 0x00aed000

Signed-off-by: Helge Deller <deller@gmx.de>