stm32l0/l1: flash: support half page flashing

Tested on L1 and L0 using the "dapboot" project, see
https://github.com/devanlai/dapboot/pull/27 for L1
and
https://github.com/devanlai/dapboot/pull/30 for L0

include/libopencm3/stm32/common/flash_common_l01.h

@@ -120,6 +120,19 @@ void flash_unlock_progmem(void);
 void flash_lock_progmem(void);
 void flash_lock_option_bytes(void);
 void flash_unlock_acr(void);
+/** Erase a page in flash.
+ * @param page_address For L1, must be first word in page, L0 doesn't care
+ * Takes 1 tprog. Flash must already be unlocked!
+ */
+void flash_erase_page(uint32_t page_address);
+
+/**
+ * Write a half page from buf to dst.
+ * This function _must_ be in ram! (See the Ref Man for more details)
+ * @param dst where to write to, expected to be aligned and erased.
+ * @param buf the half page to write, size required depends on target
+ */
+void flash_program_half_page(uint32_t *dst, void *buf);
 
 void eeprom_program_word(uint32_t address, uint32_t data);
 void eeprom_program_words(uint32_t address, uint32_t *data, int length_in_words);

include/libopencm3/stm32/l0/flash.h

@@ -55,6 +55,8 @@
 /* --- FLASH_OPTR values ----------------------------------------------------- */
 #define FLASH_OPTR_NBOOT1		(1 << 31)
 
+#define FLASH_HALF_PAGE_SIZE	16
+
 BEGIN_DECLS
 
 END_DECLS

include/libopencm3/stm32/l1/flash.h

@@ -56,7 +56,7 @@
 /* --- FLASH_SR values ----------------------------------------------------- */
 #define FLASH_SR_OPTVERRUSR		(1 << 12)
 
-/* --- Function prototypes ------------------------------------------------- */
+#define FLASH_HALF_PAGE_SIZE	32
 
 BEGIN_DECLS