the different putc variants used an initialized local static variable
which is broken since

	5de813b6 (ARM: Eliminate decompressor -Dstatic= PIC hack)

This needs to be initialized at runtime and so needs to be global.
While at it give it a better name.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>