[U-Boot] [RFC] initcall mechanism introduction

[Jean-Christophe PLAGNIOL-VILLARD]

Hi all,

	Linux Kernel has for a long time a well-optimized mechanism for for
	calling initiallisation code. Import the the same functionnality to
	U-Boot.

	Evenif it will increase a few U-Boot (999 bytes) as show in PATCH 3/3
	if we convert the NET_MULTI it will decrease of 2212 bytes at the end

Best Regards,
J.