Use correct prototype of benchmark_timer_read()

This change starts with removing the effectively empty file
timerdrv.h. The prototypes for benchmark_timer_XXX() were in
btimer.h which was not universally used. Thus every use of
timerdrv.h had to be changed to btimer.h. Then the prototypes
for benchmark_timer_read() had to be adjusted to return
benchmark_timer_t rather than int or uint32_t.

I took this opportunity to also correct the file headers to
separate the copyright from the file description comments which
is needed to ensure the copyright isn't propagated into Doxygen
output.

c/src/lib/libbsp/arm/lpc32xx/misc/timer.c

@@ -21,7 +21,6 @@
 
 #include <rtems.h>
 #include <rtems/btimer.h>
-#include <rtems/timerdrv.h>
 
 #include <bsp.h>
 
@@ -32,7 +31,7 @@ void benchmark_timer_initialize(void)
   benchmark_timer_base = lpc32xx_timer();
 }
 
-uint32_t benchmark_timer_read(void)
+benchmark_timer_t benchmark_timer_read(void)
 {
   return lpc32xx_timer() - benchmark_timer_base;
 }