stand/efi: Simplify code here

[imp]

Summary

We have plenty of stack in the EFI case, so use it instead of the
complicated malloc / free dance.

Sponsored by: Netflix

[kevans]

I had to stop a minute and consider if this is true, but it is; lua is the stack hog, and this is executing long before we get to any lua bits. We generally have to have way more than 8k stack at around this depth for lua to operate, so all is good.