spi25_statusreg: Allow WRSR_EXT for Status Register 3 (dummy part)

Spansion flash chips S25FL128L and S25FL256L use the WRSR instruction to
write more than 2 registers. So align SR2 and SR3 support: The current
FEATURE_WRSR_EXT is renamed to FEATURE_WRSR_EXT2 and FEATURE_WRSR_EXT3
is added. Also, WRSR3 needs a separate flag now.

Verified that FEATURE_WRSR_EXT2 still works using the `dummy_flasher`.

flashrom-stable:
Original patch was split, this is the `dummy_flasher.c` part.

Change-Id: I81153cb758b9fc29b803959683ad7acf8fb771e4
Signed-off-by: Nico Huber <nico.h@gmx.de>
Original-Change-Id: Ibdfc6eb3d2cfecbf8da0493d067031ddb079a094
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/64746
Original-Reviewed-by: Nikolai Artemiev <nartemiev@google.com>
Original-Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Original-Reviewed-by: Thomas Heijligen <src@posteo.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/71463
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
1 file changed