pci: Fix BAR resource sizing arbitration

According to the 'PCI Local Bus Specification, Revision 3.0,
February 3, 2004, Section 6.2.5.1, Implementation Notes, page 227'

    "Software saves the original value of the Base Address register,
    writes 0 FFFF FFFFh to the register, then reads it back. Size
    calculation can be done from the 32-bit value read by first
    clearing encoding information bits (bit 0 for I/O, bits 0-3 for
    memory), inverting all 32 bits (logical NOT), then incrementing
    by 1. The resultant 32-bit value is the memory/I/O range size
    decoded by the register. Note that the upper 16 bits of the result
    is ignored if the Base Address register is for I/O and bits 16-31
    returned zero upon read."

kvmtool was returning the actual BAR resource size which would be
incorrect as the software software drivers would invert all 32 bits
(logical NOT), then incrementing by 1. This ends up with a very large
resource size (in some cases more than 4GB) due to which drivers
assert/fail to work.

e.g if the BAR resource size was 0x1000, kvmtool would return 0x1000
instead of 0xFFFFF00x.

Fixed pci__config_wr() to return the size of the BAR in accordance with
the PCI Local Bus specification, Implementation Notes.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
[Reworked algorithm, removed power-of-two check]
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>