Platform/Sgi: Update the FILE_GUID in SgiPkgLinuxBoot.inf

Change the FILE_GUID used in SgiPkgLinuxBoot.inf to a new GUID instead
of UEFI Shell GUID.

The commit 3122d76 used the UEFI Shell GUID for the stage-1 linuxboot
kernel. The UEFI Shell GUID has been replaced with a new GUID since we
are going to use LinuxBootBootManager Library instance which adds
stage-1 linuxboot kernel as valid boot option. Hence, replacing the UEFI
shell binary with the stage-1 linux kernel by using the UEFI Shell GUID
in SgiPkgLinuxBoot.inf is no longer needed.

Signed-off-by: Shriram K <shriram.k@arm.com>
Change-Id: If40d4087ab1566fbb947e287a10d3fbb765bbb9b