Move timing functions to internal memory

The implementation of sleep_cycles has cycle-accurate predictions for
function call overhead. These can only be fulfilled if it never requires
fetching from extmem.

Change-Id: Idc5fe1571c751bfed0889db4906531a073ef2949

include/libnux/vx/spr.h

@@ -36,7 +36,9 @@ SPR_GETTER(get_tbl, "mfspr %0, 284")
 
 typedef uint64_t time_base_t;
 
-ATTRIB_UNUSED static time_base_t get_time_base() {
+ATTRIB_UNUSED static time_base_t get_time_base() ATTRIB_LINK_TO_INTERNAL;
+static time_base_t get_time_base()
+{
 	time_base_t tbu, tbl;
 	tbu = get_tbu();
 	tbl = get_tbl();

include/libnux/vx/time.h

@@ -12,7 +12,7 @@ namespace libnux::vx {
 
 constexpr static uint32_t default_ppu_cycles_per_us = 250;
 
-void sleep_cycles(uint32_t cycles);
+void sleep_cycles(uint32_t cycles) ATTRIB_LINK_TO_INTERNAL;
 
 /*
 	Get current absolute time in ppu cycles.