Fix a cluster of bugs in list EFI environment variables:

Fix a cluster of bugs in list EFI environment variables:
1. Size returned for variable name is in bytes, not CHAR16 (the
   UEFI standard is unclear on this, where it is clear on the size of
   the variable).
2. Dynamically allocate the buffers so we can grow them if someone
   defines a super-long variable name.

These two fixes allow me to examine all the variables in my BIOS and
also removes the repeated printing of variables.