[efi] Do not assume canonical PE section ordering

[efi] Do not assume canonical PE section ordering

The BaseOfCode (and, in PE32, BaseOfData) fields imply an assumption
that binaries are laid out as code followed by initialised data
followed by uninitialised data.  This assumption may not be valid for
complex binaries such as wimboot.

Remove this implicit assumption, and use arguably justifiable values
for the assorted summary start and size fields within the PE headers.

Signed-off-by: Michael Brown <mcb30@ipxe.org>