STM32 Timer: Generalize and extend calculation of per-timer pre-scaler value.  Inspired by original proposal from Pierre-noel Bouteville.

This reverts commit 082d3222.

Remove drivers/mtd/flash_eraseall.c.  It is not used in the OS and is just a dumb wrapper around the MDIOC_BULKERASE IOCTL call.

Fix the Value Line adc IRQ number selection

STM32F4 RTC: Remove 24 hour limit; Fix calculation of the alarm register (was not including day of the month).  Fix a bad shift value

The rtc examples "alarm 10" now runs to completion

correct bugs and add enhancements to pcf8574 lcd backpack driver

fleshed out rest of fileops interface; read now takes into consideration current file position (so the display can be read in multiple operations, and indiate EOF correctly), seek (really just to facilitate rewind), and unlink (to facilitate dropping from system at runtime).