efi_loader: optional data in load options are binary

efi_loader: optional data in load options are binary

The field boot OptionalData in structure _EFI_LOAD_OPTIONS is for binary
data.

When we use `efidebug boot add` we should convert the 5th argument from
UTF-8 to UTF-16 before putting it into the BootXXXX variable.

When printing boot variables with `efidebug boot dump` we should support
the OptionalData being arbitrary binary data. So let's dump the data as
hexadecimal values.

Here is an example session protocol:

=> efidebug boot add 00a1 label1 scsi 0:1 doit1 'my option'
=> efidebug boot add 00a2 label2 scsi 0:1 doit2
=> efidebug boot dump
Boot00A0:
  attributes: A-- (0x00000001)
  label: label1
  file_path: .../HD(1,MBR,0xeac4e18b,0x800,0x3fffe)/doit1
  data:
    00000000: 6d 00 79 00 20 00 6f 00 70 00 74 00 69 00 6f 00  m.y. .o.p.t.i.o.
    00000010: 6e 00 00 00                                      n...
Boot00A1:
  attributes: A-- (0x00000001)
  label: label2
  file_path: .../HD(1,MBR,0xeac4e18b,0x800,0x3fffe)/doit2
  data:

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>