Introduce x86_linux_update_debug_registers

Introduce x86_linux_update_debug_registers

This commit moves the entire body of both GDB's and gdbserver's
x86_linux_prepare_to_resume functions into new functions,
x86_linux_update_debug_registers.  This reorganisation allows
all Linux x86 low-level debug register code to be placed in one
shared file, separate from general Linux x86 shared code.

gdb/ChangeLog:

	* x86-linux-nat.c (x86_linux_update_debug_registers):
	New function, factored out from...
	(x86_linux_prepare_to_resume): ...this.

gdb/gdbserver/ChangeLog:

	* linux-x86-low.c (x86_linux_update_debug_registers):
	New function, factored out from...
	(x86_linux_prepare_to_resume): ...this.