When I ran the Windows 8 upgrade assistant, it said secure boot is not available for my PC firmware. I am using Dell XPS 17 L702 on 64-bit. Since I dual boot Linux as well, Is there a way to have the secure boot option available?
AFAIK secure boot will not allow to boot Linux, there are plans sign a bootloader which in turn would load existing bootloaders(e.g. GRUB), but it's not done yet. If you still want to enable it:
Secure boot is something baked into the UEFI bootloader (calling it a 'bios' would be inaccurate but it does the same thing) and is an option the OEM needs to enable. If your system dosen't have it already, you'd likely need a new UEFI version that supports it for your PC.
You can't just turn it 'on' on an existing system, and chances are unless you buy a system with windows 8 preinstalled and secure boot in place, you can't 'just' enable it
Secure boot is a technology described by recent revisions of the UEFI specification; it offers the prospect of a hardware-verified, malware-free operating system and improve the security of many system deployments.
The Linux Foundation has come up with a solution that should work for any and all operating systems.
When Linux Foundation is able to obtain a SecureBoot key from Microsoft, they will release this new pre-bootloader on their web-site.
You probably have to update your motherboard "BIOS". That is what I had to do with my "DELL Vostro 470" PC that I had bought in June. I suggest that you go to the DELL website and go to the "Driver Download" section to find out whether your PC is suitable for an update. You will need your DELL Service Tag information. If you do an upgrade be very careful not to interrupt the process. You could leave the motherboard in an inoperable state. After the update the default state is "Secure Boot Disabled". On my PC I repeatedly hit the F12 key during power up to get into the "Boot Option menu" where I could change that to Secure Boot Enabled and also change to make my CD drive the first boot device instead of the HDD.