MIPS: BCM63XX: drop unused and broken DSP platform device

MIPS: BCM63XX: drop unused and broken DSP platform device

Trying to register the DSP platform device results in a null pointer
access:

[    0.124184] CPU 0 Unable to handle kernel paging request at virtual address 00000000, epc == 804e305c, ra == 804e6f20
[    0.135208] Oops[#1]:
[    0.137514] CPU: 0 PID: 1 Comm: swapper Not tainted 4.14.87
...
[    0.197117] epc   : 804e305c bcm63xx_dsp_register+0x80/0xa4
[    0.202838] ra    : 804e6f20 board_register_devices+0x258/0x390
...

This happens because it tries to copy the passed platform data over the
platform_device's unpopulated platform_data.

Since this code has been broken since its submission, no driver was ever
submitted for it, and apparently nobody was using it, just remove it
instead of trying to fix it.

Fixes: e7300d04bd08 ("MIPS: BCM63xx: Add support for the Broadcom BCM63xx family of SOCs.")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>