xen/x86: switch to use generic implemetation of bug.h

xen/x86: switch to use generic implemetation of bug.h

The following changes were made:
* Make GENERIC_BUG_FRAME mandatory for X86
* Update asm/bug.h using generic implementation in <xen/bug.h>
* Update do_invalid_op using generic do_bug_frame()
* Define BUG_DEBUGGER_TRAP_FATAL to debugger_trap_fatal(X86_EXC_GP,regs)
* type of eip variable was changed to 'const void *'

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>