arch: arm: core: cortex_a_r: enable the VFP unit on boot for FPU_SHARING

The FPU is already disabled by the z_arm_svc function when the first
thread starts. Therefore, disabling the FPU at boot is unnecessary for
lazy FPU; instead, it must be enabled to handle floating-point instructions
before the lazy FPU works.

Signed-off-by: Ha Duong Quang <ha.duongquang@nxp.com>