ACPI: GTDT: Tighten the check for the array of platform timer structures

As suggested by Marc and Lorenzo, first we need to check whether the
platform_timer entry pointer is within gtdt bounds (< gtdt_end) before
de-referencing what it points at to detect the length of the platform
timer struct and then check that the length of current platform_timer
struct is also valid, i.e. the length is not zero and within gtdt_end.
Now next_platform_timer() only checks against gtdt_end for the entry of
subsequent platform timer without checking the length of it and will
not report error if the check failed and the existing check in function
acpi_gtdt_init() is also not enough.

Modify the for_each_platform_timer() iterator and use it combined with
a dedicated check function platform_timer_valid() to do the check
against table length (gtdt_end) for each element of platform timer
array in function acpi_gtdt_init(), making sure that both their entry
and length actually fit in the table.

Suggested-by: Lorenzo Pieralisi <[email protected]>
Co-developed-by: Marc Zyngier <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Signed-off-by: Zheng Zengkai <[email protected]>
Reviewed-by: Lorenzo Pieralisi <[email protected]>
Reviewed-by: Hanjun Guo <[email protected]>
Tested-by: Hanjun Guo <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

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