ARM: OMAP2+: UART: cleanup + remove uart pm specific API

In preparation to UART runtime conversion remove uart specific calls
from pm24xx/34xx files and their definition from serial.c
These func calls will no more be used with upcoming uart runtime design.

1.) omap_uart_prepare_suspend :- can be taken care with driver suspend hooks.
2.) omap_uart_enable_irqs :- Used to enable/disable uart irq's in suspend
    path from PM code, this is removed as same is handled by
    uart_suspend_port/uart_resume_port in omap-serial driver which will
    do an port_shutdown on suspend freeing irq and port_startup on resume
    enabling back irq.
3.) Remove prepare_idle/resume_idle calls used to gate uart clocks.
    UART clocks can be gated within driver using runtime funcs
    and be woken up using irq_chaining from omap_prm driver.
4.) Remove console_locking from idle path as clock gating is done withing
    driver itself with runtime API. Remove is_suspending check used to acquire
    console_lock.

Signed-off-by: Govindraj.R <govindraj.raja@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>