[PowerPC] Fix offset calculations in bridge mode

[bdragon]

Summary

In rS354701, I replaced text relocations with offsets from &generictrap.

Unfortunately, the magic variable I was using doesn't actually mean the address of &generictrap, in bridge mode it actually means &generictrap64.

So, for bridge mode to work, it is necessary to differentiate between "where do we need to branch to to handle a trap" and "where is &generictrap for purposes of doing relative math".

Introduce a new TRAP_ENTRY and use it instead of TRAP_GENTRAP for doing actual calls to the generic trap handler.

Unfortunately, bridge mode is still broken even with this change due to the memory corruption problem.

[jhibbits]

sys/powerpc/include/trap.h

150 ↗

(On Diff #66420)

Is 0x1e8 taken?

[bdragon]

sys/powerpc/include/trap.h

150 ↗

(On Diff #66420)

Nope, I just apparently can't count backwards in hex.

[bdragon]

Use different address. I meant to have them next to each other but I jumped from f to d.

[bdragon]

I *meant* to alphabetize this in the first place.
This puts TRAP_GENTRAP back at its original address, too.