Cleanup ST M50 driver

There are two locking strategies used by this umbrella family, one uniform
and one that matches the sector layout of the chip. Refactor the functions
involved and rename the overly complicated file to just stm50.c and the
functions accordingly.

This fixes unlocking of some of the non-uniform chips and gets rid of the
abuse of page_size.

Corresponding to flashrom svn r1736.

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
diff --git a/82802ab.c b/82802ab.c
index 608995d..2a43813 100644
--- a/82802ab.c
+++ b/82802ab.c
@@ -89,6 +89,7 @@
 	return 1;
 }
 
+/* FIXME: needs timeout */
 uint8_t wait_82802ab(struct flashctx *flash)
 {
 	uint8_t status;