USB: musb: add musb support for AM35x

USB: musb: add musb support for AM35x

AM35x has musb interface and uses CPPI4.1 DMA engine.
Current patch supports only PIO mode. DMA support can be
added later once basic CPPI4.1 DMA patch is accepted.

Also added USB_MUSB_AM35X which is required to differentiate musb ips
between OMAP3x and AM35x. This config would be used to for below
purposes,
        - Select am35x.c instead of omap2430.c for compilation
          at drivers/usb/musb directory. Please note there are
          significant differneces in these two files as musb ip
          in quite different on AM35x.

	  Please note that in multi omap configuration only omap2430.c
	  file will get compiled and we would require to select only
	  AM35x based board config to compile am35x.c

        - Select workaround codes applicable for AM35x musb issues.
          one such workaround is for bytewise read issue on AM35x.

Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>