Add additional fdt fixup helper functions

Added the following fdt fixup helpers:
 * do_fixup_by_prop{_u32} - Find matching nodes by property name/value
 * do_fixup_by_compat{_u32} - Find matching nodes by compat

The _u32 variants work the same only the property they are setting
is know to be a 32-bit integer instead of a byte buffer.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>