lib: provide a simple generic ioremap implementation

A lot of architectures reuse the same simple ioremap implementation, so
start lifting the most simple variant to lib/ioremap.c.  It provides
ioremap_prot and iounmap, plus a default ioremap that uses prot_noncached,
although that can be overridden by asm/io.h.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Palmer Dabbelt <palmer@dabbelt.com>
diff --git a/lib/Kconfig b/lib/Kconfig
index 3321d04..cb57176 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -637,6 +637,9 @@
 
 endmenu
 
+config GENERIC_IOREMAP
+	bool
+
 config GENERIC_LIB_ASHLDI3
 	bool