mfd: Fix modular builds of rc5t583 regulator support

The combination of commit 1b1247dd

    "mfd: Add support for RICOH PMIC RC5T583"

and commit 6ffc3270

    "regulator: Add support for RICOH PMIC RC5T583 regulator"

are causing the i386 allmodconfig builds to fail with this:

  ERROR: "rc5t583_update" [drivers/regulator/rc5t583-regulator.ko] undefined!
  ERROR: "rc5t583_set_bits" [drivers/regulator/rc5t583-regulator.ko] undefined!
  ERROR: "rc5t583_clear_bits" [drivers/regulator/rc5t583-regulator.ko] undefined!
  ERROR: "rc5t583_read" [drivers/regulator/rc5t583-regulator.ko] undefined!

and this:

  ERROR: "rc5t583_ext_power_req_config" [drivers/regulator/rc5t583-regulator.ko] undefined!

For the 1st four, make the simple ops static inline, instead of
polluting the namespace with trivial exports.  For the last one,
add an EXPORT_SYMBOL.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>