davinci: DM644x EVM: register MUSB device earlier

The MUSB driver doesn't see its platform device on DM644x EVM board anymore
since commit 73b089b0 (usb: musb: split davinci
to its own platform_driver) because the new probe is called as subsys_initcall()
now, and the device is registered later than that by the board code.  Move the
registration to davinci_evm_init() -- it's safe to do so because the MUSB core
device still gets initialized as fs_initcall() -- which is late enough for the
I2C GPIO expander (which controls VBUS) to be initialized.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Tested-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>