timestamps: Rename timestamps to make names more consistent

This patch aims to make timestamps more consistent in naming,
to follow one pattern. Until now there were many naming patterns:
- TS_START_*/TS_END_*
- TS_BEFORE_*/TS_AFTER_*
- TS_*_START/TS_*_END
This change also aims to indicate, that these timestamps can be used
to create time-ranges, e.g. from TS_BOOTBLOCK_START to TS_BOOTBLOCK_END.

Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Change-Id: I533e32392224d9b67c37e6a67987b09bf1cf51c6
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62019
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/lib/hardwaremain.c

@@ -457,7 +457,7 @@ void main(void)
 	 */
 	cbmem_initialize();
 
-	timestamp_add_now(TS_START_RAMSTAGE);
+	timestamp_add_now(TS_RAMSTAGE_START);
 	post_code(POST_ENTRY_HARDWAREMAIN);
 
 	/* Handoff sleep type from romstage. */