bcma: don't leak memory for PCIE, MIPS, GBIT cores

bcma_scan_bus allocates a bcma_core for each core found on the bus, but the
memory for cores handled by the bcma driver itself was not being freed when
the bus was unregistered. This patch adds special handling for the PCIE,
MIPS, and GBIT COMMON cores, to ensure that their memory allocation is
freed as well.

Note that this patch doesn't address the memory allocated for the CC core,
as that was corrected in my previous patch "bcma: register cc core driver,
device."

Cc: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Saul St. John <saul.stjohn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>