asm-generic/u-boot.h: make <asm-generic/u-boot.h> self-contained

This header uses 'phys_addr_t' and 'ulong'. Include the definitions.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
[trini: Move include to below __ASSEMBLY__ test]
Signed-off-by: Tom Rini <trini@konsulko.com>