[ARM] pxa: remove un-used pxa3xx_mfp_set_xxx() functions

pxa3xx_mfp_set_xxx() functions are originally provided for overwriting
MFP configurations performed by pxa3xx_mfp_config(), the usage of such
a dirtry trick is not recommended, since there is currently no user of
these functions, they are safely removed

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>