drm/i915: Check for integer truncation on the configuration of ttm place

There is an impedance mismatch between the first/last valid page
frame number of ttm place in unsigned and our memory/page accounting in
unsigned long.
As the object size is under the control of userspace, we have to be prudent
and catch the conversion errors.
To catch the implicit truncation as we switch from unsigned long to
unsigned, we use overflows_type check and report E2BIG or overflow_type
prior to the operation.

v3: Not to change execution inside a macro. (Mauro)
    Add safe_conversion_gem_bug_on() macro and remove temporal
    SAFE_CONVERSION() macro.
v4: Fix unhandled GEM_BUG_ON() macro call from safe_conversion_gem_bug_on()
v6: Fix to follow general use case for GEM_BUG_ON(). (Jani)
v7: Fix to use WARN_ON() macro where GEM_BUG_ON() macro was used. (Jani)
v8: Replace safe_conversion() with check_assign() (Kees)
v14: Split one macro of assignment with checking of overflow to two steps,
     first overflow check, and second assignment.

Cc: Chris Wilson <[email protected]>
Cc: Matthew Auld <[email protected]>
Cc: Thomas Hellström <[email protected]>
Cc: Jani Nikula <[email protected]>
Signed-off-by: Gwan-gyeong Mun <[email protected]>
Reviewed-by: Nirmoy Das <[email protected]> (v2)
Reviewed-by: Mauro Carvalho Chehab <[email protected]> (v3)
Reported-by: kernel test robot <[email protected]>
Reviewed-by: Andrzej Hajda <[email protected]> (v5)
Signed-off-by: Rodrigo Vivi <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

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