libpayload: timer: Revert timer_hz() return type to 64-bits

It seems that reducing the return type of timer_hz() to uint32_t in
CB:78888 was a bad idea... some Intel platforms actually use their raw
CPU clock for the timestamp counter which can be higher than 4GHz. This
patch reverts it back to uint64_t.

Also remove the redundant assertion in timer/generic.c since timer_us()
itself already does that check.

Cq-Depend: chromium:5274555
Change-Id: I471c7de7a28aec5bb965b23525ed579481ac8361
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80320
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Yidi Lin <yidilin@google.com>

payloads/libpayload/drivers/timer/generic.c

@@ -33,10 +33,8 @@
 #include <assert.h>
 #include <libpayload.h>
 
-uint32_t timer_hz(void)
+uint64_t timer_hz(void)
 {
-	/* libc/time.c currently requires all timers to be at least 1MHz. */
-	assert(CONFIG_LP_TIMER_GENERIC_HZ >= 1000000);
 	return CONFIG_LP_TIMER_GENERIC_HZ;
 }