stm32: timer/dmamux: fix broken includes

bad Karl, you can't just _start_ using pragma on common files, and
expect it to keep working.  Just finish, convert them fully to pragma.

pros: no more weird @cond boilerplate mess and trailing #endifs. easier
to follow
cons: no warning for people who deliberately try and include things in
bad orders.

include/libopencm3/stm32/l0/timer.h

@@ -33,7 +33,6 @@ LGPL License Terms @ref lgpl_license
  */
 
 #pragma once
-
 #include <libopencm3/stm32/common/timer_common_all.h>
 
 /**@{*/
@@ -96,4 +95,3 @@ LGPL License Terms @ref lgpl_license
 #define TIM22_OR_TI1_RMP_COMP1_OUT	(2 << TIM22_OR_TI1_RMP_SHIFT)
 
 /**@}*/
-