spl: consolidate arch/arm/include/asm/arch-*/spl.h

spl: consolidate arch/arm/include/asm/arch-*/spl.h

arch/arm/include/asm/spl.h requires all SoCs to have
arch/arm/include/asm/arch-*/spl.h.

But many of them just define BOOT_DEVICE_* macros.

Those macros are used in the "switch (boot_device) { ... }"
statement in common/spl/spl.c.

So they should not be archtecture specific, but be described as
a simpile enumeration.

This commit merges most of arch/arm/include/asm/arch-*/spl.h
into arch/arm/include/asm/spl.h.

With a little more effort, arch-zynq/spl.h and arch-socfpga/spl.h
will be merged, while I am not sure about OMAP and Exynos.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Tom Rini <trini@ti.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Andreas Bießmann <andreas.devel@googlemail.com>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Tom Warren <twarren@nvidia.com>
CC: Stefano Babic <sbabic@denx.de>
CC: Minkyu Kang <mk7.kang@samsung.com>
Cc: Dinh Nguyen <dinguyen@altera.com>
Acked-by: Andreas Bießmann <andreas.devel@googlemail.com>
Acked-by: Michal Simek <monstr@monstr.eu>
Acked-by: Stefano Babic <sbabic@denx.de>
Acked-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Tim Harvey <tharvey@gateworks.com>
Tested-by: Bo Shen <voice.shen@atmel.com> [on sama5d3xek board for at91 part]
Acked-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stefano Babic <sbabic@denx.de> [applying Tim's i.MX6 patches]
Acked-by: Tom Rini <trini@ti.com>