cr50: rename a power-button press ISR.
cr50: rename a power-button press ISR.

crrev.com/c/1192691 added power_button_release_enable_interrupt()
but didn't rename power_button_enable_interrupt().  This CL renames
one of them to keep them symmetric.

BRANCH=cr50
BUG=b:37351386
TEST=none

Change-Id: I96a7705ba2684b26410618f177a95201d2ee0683
Signed-off-by: Namyoon Woo <e8732cefb861f07768f47df788a8e8eb75efc09a@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1268856
Reviewed-by: Mary Ruthven <81380f3403fed74252e92df3ed012a1819ec6296@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec