[efi] Allow for sections to be excluded from the generated PE file

[efi] Allow for sections to be excluded from the generated PE file

Hybrid bzImage and UEFI binaries (such as wimboot) include a bzImage
header within a section starting at offset zero, with the PE header
effectively occupying unused space within this section.  This section
should not appear as a named section in the resulting PE file.

Allow for the existence of hidden sections that do not result in a
section header being written to the PE file.

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