tree/: Convert flashchip read func ptr to enumerate

This forges the way for flashchips.c to be pure declarative
data and lookup functions for dispatch to be pure. This
means that the flashchips data could be extracted out to
be agnostic data of the flashrom code and algorithms.

Squash in,
flashchips.c: convert edi_chip_read()
flashchips.c: convert spi_chip_read()
flashchips.c: convert read_opaque()
flashchips.c: convert read_memmapped()
flashchips.c: convert spi_read_at45db_e8()
flashchips.c: convert spi_read_at45db()
flashchips.c: convert NULL cases

Change-Id: I612d46fefedf2b69e7e2064aa857fa0756efb4e7
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
---
M flashchips.c
M flashrom.c
M fmap.c
M include/flash.h
M libflashrom.c
M tests/chip.c
M tests/chip_wp.c
7 files changed, 678 insertions(+), 606 deletions(-)