ich_descriptors: Revise detection for chipsets w/ ICCRIBA

Detection based on ICCRIBA and FMSBA became a little messy lately.
However, there's a new static difference: Since 300 series (Cannon
Point), there is an MDTBA field in FLUMAP1 that has always been 0
(reserved) before. Taking this into account, we can relax the checks
on ICCRIBA.

Change-Id: I587ad1abe390843d4a9e74431b6fc4b63f8ba512
Signed-off-by: Nico Huber <nico.h@gmx.de>
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M ich_descriptors.c
M ich_descriptors.h
2 files changed, 26 insertions(+), 22 deletions(-)