MIPS: new Kconfig option ZBOOT_LOAD_ADDRESS

If this option is not 0x0, it will be used for zboot load address.
Otherwise, the result of calc_vmlinuz_load_addr will be used.

The zload-y value for generic are also removed then, as the current
value breaks booting on qemu -M boston.
The result of calc_vmlinuz_load_addr works well for most of cases.

The default value of bcm47xx keeps as it currently.

Signed-off-by: YunQiang Su <yunqiang.su@cipunited.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

MIPS: Only include the platform file needed

Instead of including all Platform files, we simply include the
needed one and avoid clashes with makefile variables.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

MIPS: bcm47xx: enable ZBOOT support

Enable ZBOOT support. The WRT54GL router's bootloader limits kernel
size to 3 MB with the normal load address, which is a bit challenging
vmlinux size with modern Linux. A compressed kernel allows booting
much bigger kernels.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18492/
Signed-off-by: James Hogan <jhogan@kernel.org>

MIPS: BCM47xx: Migrate to new platform makefile style.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>