x86/desc: Shorten boot_{,compat_}gdt[] variable names

x86/desc: Shorten boot_{,compat_}gdt[] variable names

The current names, boot_cpu_{,compat_}gdt_table, have a table suffix which is
redundant with the T of GDT, and the cpu infix doesn't provide any meaningful
context.  Drop them both.

Likewise, shorten the {,compat_}gdt{,_l1e} variables.

Finally, rename gdt_descr to boot_gdtr to more clearly identify its purpose.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>