Return an error if the maximum numbers of partitions has been
reached and thus creating further partitions would result in
errors.
Currently we limit MBR partition types to 4 as we dont support
logical partitions and GPT layouts to 128. According to the
UEFI specificatio (2.8) a minimum of 16384 bytes are reserved
for the partition entries array. Each entry is 128 bytes wide
thus resulting in at least 128 entries; we choose this to be
the maximum as well for now.
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