remoteproc: adopt the driver core's alloc/add/del/put naming

To make remoteproc's API more intuitive for developers, we adopt
the driver core's naming, i.e. alloc -> add -> del -> put. We'll also
add register/unregister when their first user shows up.

Otherwise - there's no functional change here.

Suggested by Russell King <linux@arm.linux.org.uk>.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Fernando Guzman Lugo <fernando.lugo@ti.com>
Cc: Sjur Brændeland <sjur.brandeland@stericsson.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>