PCI: Push realloc check into pbus_size_mem()

pbus_size_mem() and calculate_memsize() input both min_size and add_size.
They are given the same value if realloc_head is NULL and min_size is 0
otherwise. Both are used in calculate_memsize() to enforce a lower bound to
the size.

The interface between __pci_bus_size_bridges() and the forementioned
functions can be simplied by pushing the realloc check into
pbus_size_mem().

There are only two possible cases:

1) when calculating size0, add_size parameter given to
calculate_memsize() is always 0 which implies only min_size
matters.

2) when calculating size1, realloc_head is not NULL which implies
min_size=0 so only add_size matters.

Drop min_size parameter from pbus_size_mem() and check realloc_head when
calling calculate_memsize(). Drop add_size from calculate_memsize() and use
only min_size within max() to enforce the lower bound.

calculate_iosize() is a bit more complicated than calculate_memsize() and
is therefore left as is, but pbus_size_io() can still input only min_size
similar to pbus_size_mem().

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20251219174036.16738-7-ilpo.jarvinen@linux.intel.com